Screw Compressor

Abstract

To provide a screw compressor that expands a range where a liquid supply mechanism can be installed.SOLUTION: A screw compressor includes: screw rotors 21, 22; a casing for accommodating the screw rotors 21, 22; and a liquid supply mechanism for supplying liquid to an operation chamber that is encapsulated by the casing. The screw rotors 21, 22 have a pitch that varies in an axial direction toward a discharge end surface from a suction end surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a liquid-feed screw compressor. [Background technology]

[0002] Some screw compressors are operated while supplying liquid to the working chamber. It is known that supplying liquid lubricates the screw rotor and at the same time cools the working fluid and suppresses internal leakage. On the other hand, the rotating screw rotor requires power to transport the supplied liquid to the discharge port, which reduces the energy-saving performance of the compressor.

[0003] As an example of a countermeasure against increased power consumption, Patent Document 1 describes a technology in which the cooling efficiency of an oil-lubricated screw compressor is improved by efficiently diffusing the oil supplied, thereby efficiently cooling the compressed air with a small amount of oil injection and reducing the oil agitation loss caused by the screw rotor.

[0004] In addition, in the case of a general liquid supply by differential pressure, the possible installation position of the liquid supply port is limited to a location that communicates with a working chamber with a lower pressure than the liquid supply source pressure. In addition, in order to satisfy the required amount of liquid supply, the pressure difference between the liquid supply source pressure and the pressure of the working chamber to which the liquid supply port communicates must be sufficiently large, which limits the possible installation range of the liquid supply port. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2001-153073 Summary of the Invention [Problem to be solved by the invention]

[0006] In a liquid-feed type screw compressor, the minimum amount of liquid feed required to lubricate the screw rotor is fixed, so there is a limit to reducing the churning loss by the method of reducing the amount of liquid feed as described in Patent Document 1. Therefore, in order to reduce the churning loss without changing the amount of liquid feed, it is effective to take measures to move the liquid feed port closer to the discharge port, but this has the problem of limiting the range in which the liquid feed port can be installed.

[0007] Moreover, in recent years, as compressors have become faster and more compact, the screw rotor and casing have become smaller, reducing the area in which liquid supply ports can be installed, posing an issue of reduced design freedom in terms of the number and location of liquid supply ports.

[0008] The present inventors have discovered that when the pitch of the screw rotor changes, the range in which the liquid supply port can be installed can be expanded.

[0009] An object of the present invention is to provide a screw compressor which expands the range in which a liquid supply mechanism can be installed. [Means for solving the problem]

[0010] As a preferred example of the present invention, a liquid supply mechanism is provided that supplies liquid to a working chamber surrounded by a screw rotor, a casing that houses the screw rotor, and the screw rotor is From suction end face to discharge end face The pitch is in the axial direction from the suction end face to the discharge end face. Monotonically increasing It is a screw compressor. Effect of the Invention

[0011] According to the present invention, the range in which the liquid supply mechanism can be installed can be expanded. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a side view of the screw rotor in the first embodiment. [Diagram 2] FIG. 1 is a configuration diagram of a screw compressor. [Diagram 3] 2 is a cross-sectional view taken along line AA in FIG. 1. [Figure 4] FIG. 1 is a diagram showing an oil supply path of a typical screw compressor. [Diagram 5] FIG. 1(a) is a side view of a screw rotor with variable pitch in Example 1, and FIG. 1(b) is a side view of a screw rotor with a constant pitch that is the same as the screw rotor in (a) in terms of cross-sectional shape perpendicular to the axial direction of the screw rotor, etc. [Figure 6] FIG. 6(a) is a side view of a screw rotor with variable pitch in the first embodiment having a different rotation angle from that in FIG. 5, and FIG. 6(b) is a side view of a screw rotor with a constant pitch having the same cross-sectional shape perpendicular to the axial direction of the screw rotor as the screw rotor in FIG. 6(a). [Figure 7] FIG. 11 is a side view of the screw rotor in the second embodiment. [Figure 8] FIG. 11 is a cross-sectional view of a liquid supply nozzle in the second embodiment. [Figure 9] FIG. 11 is a cross-sectional view of a liquid supply nozzle in the second embodiment. [Figure 10] 13 is a diagram showing a connection portion between a slit portion and a working space in the second embodiment. FIG. [Figure 11] FIG. 10(a) is a side view of a screw rotor with variable pitch in Example 3, and FIG. 10(b) is a side view of a screw rotor with a constant pitch that is the same as the screw rotor in (a) in terms of cross-sectional shape perpendicular to the axial direction of the screw rotor, etc. [Figure 12] 11. (a) is a side view of a screw rotor with variable pitch in Example 3, which has a different rotation angle from that in FIG. 11, and (b) is a side view of a screw rotor with a constant pitch, which is the same as the screw rotor in (a) in terms of the shape of a cross section perpendicular to the axial direction of the screw rotor, etc. [Figure 13] FIG. 11 is a side view of a screw rotor with variable pitch in the third embodiment. [Figure 14] FIG. 11 is a side view of a screw rotor with variable pitch in the fourth embodiment. [Figure 15]4 is a graph showing the relationship between the distance from the suction end face of the working chamber and the pressure in the first embodiment. [Figure 16] 11 is a graph showing the relationship between the distance from the suction end face of the working chamber and the pressure in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Prior to describing the embodiments, the overall configuration of the screw compressor will be described. The configuration of the screw compressor is shown in Figures 2 and 3. Figure 2 is a configuration diagram of the screw compressor, and Figure 3 is a cross-sectional view taken along the line AA in Figure 2.

[0014] The screw compressor 1 is composed of a screw rotor equipped with a male screw rotor 2 and a female screw rotor 3 that have twisted teeth (lobes) and rotate while meshing with each other, a casing 4 that houses them, a suction side bearing 5 and a discharge side bearing 6 for supporting both the male and female screw rotors respectively so that they can rotate freely, and shaft sealing parts 7 such as oil seals or mechanical seals.

[0015] Typically, the male screw rotor 2 is connected to a motor 8, which is a rotation drive source, via a screw rotor shaft at the suction end. The male screw rotor 2 and the female screw rotor 3 are housed in a male bore 9 and a female bore 10 of a casing 4, respectively, with a gap of several tens to several hundreds of μm maintained.

[0016] Here, the axial direction of the screw rotor is the direction indicated by E in FIG.

[0017] The male screw rotor 2, rotated by the motor 8, rotates the female screw rotor 3, and the working space 11 formed by the tooth grooves of both the male and female screw rotors and the male bore 9 and female bore 10 surrounding them expands and contracts, sucking in a fluid such as air through the suction port 12, compressing it to a predetermined pressure, and then discharging it from the discharge flow path 13.

[0018] In addition, liquid is injected into the working space 11, the suction side bearing 5, the discharge side bearing 6, and the shaft seal component 7 from outside the screw compressor 1 through the liquid supply port 14, the suction side bearing liquid supply port 15, and the discharge side bearing liquid supply port 16.

[0019] In FIG. 3, reference numeral 14a denotes a liquid supply port of the male bore, and reference numeral 14b denotes a liquid supply port of the female bore.

[0020] 4 shows the external path of the liquid supplied to the screw compressor 1. The liquid path is made up of the screw compressor 1, a centrifugal separator 17, a cooler 18, auxiliary equipment 19 such as a filter and a check valve, and piping 20 connecting them.

[0021] Liquids such as oil or water injected from the outside into the compressor are mixed in the compressed gas discharged from the screw compressor 1. The liquid mixed in the compressed gas is separated from the compressed gas by a centrifugal separator 17, cooled by a cooler 18, and then branched off via an auxiliary device 19, and is again supplied from a liquid supply port 14 to the working space 11 inside the screw compressor 1, from a suction side bearing liquid supply port 15 to the suction side bearing 5, and from a discharge side bearing liquid supply port 16 to the discharge side bearing 6.

[0022] The branching point of the liquid path is not limited to the outside of the screw compressor 1 as shown in FIG. 4, but may also branch inside the casing 4 of the screw compressor 1.

[0023] In this embodiment, by expanding the range in which the liquid supply port can be installed in such a screw compressor, it is possible to obtain effects such as reducing the agitation loss and increasing the cooling efficiency, thereby providing a screw compressor with high energy-saving performance.

[0024] The screw rotors in Figures 2 and 3 are typical screw rotors in which the pitch, which is the distance between the lobes of the screw rotor, does not change. In the examples, the screw rotors in Figures 2 and 3 are common to all but the screw rotors, but the screw rotors differ from example to example, and the pitch also changes from the suction end face to the discharge end face.

[0025] Here, the suction end face refers to the end face of the female or male screw rotor that is closer to the suction port 12 in Fig. 2. The discharge end face refers to the end face of the female or male screw rotor that is closer to the discharge flow passage 13 in Fig. 2. EXAMPLES

[0026] A first embodiment will be described with reference to Figures 1, 2, 3, 5, 6, and 15. This embodiment relates to a liquid supply type screw air compressor. In the description of this embodiment, the same parts as those described above will be denoted by the same reference numerals.

[0027] In this embodiment, the male screw rotor 2 and female screw rotor 3 shown in Fig. 3 are the variable pitch male screw rotor 21 and variable pitch female screw rotor 22 shown in Fig. 1, respectively, and a drilled hole liquid supply port 27 is provided on the discharge end face side of plane C shown in Fig. 1. The variable pitch male screw rotor 21 and variable pitch female screw rotor 22 are screw rotors whose pitch increases from the suction end face towards the discharge end face, i.e., in the axial direction of the screw rotor.

[0028] Fig. 5(a) shows a male screw rotor 21 with a variable pitch and a female screw rotor 22 with a variable pitch as viewed from direction B in Fig. 2, with the upper side being the suction end face and the lower side being the discharge end face. In order to compare the screw rotor of this embodiment with a conventional screw rotor, Fig. 5(b) shows a male screw rotor 23 with a uniform pitch and a female screw rotor 24 with a uniform pitch as viewed from direction B in Fig. 2.

[0029] However, the male screw rotor 23 with equal pitch is defined as a screw rotor whose pitch does not change from the suction end face to the discharge end face, and which is equivalent to the male screw rotor 21 with variable pitch in terms of the shape and dimensions of the cross section perpendicular to the screw rotor axis, the screw rotor length, and the total wrap angle.

[0030] The equal-pitch female screw rotor 24 is defined as a screw rotor whose pitch does not change from the suction end face to the discharge end face, and which is equal to the variable-pitch female screw rotor 22 in terms of the shape and dimensions of the cross section perpendicular to the screw rotor axis, the screw rotor length, and the total wrap angle.

[0031] In this way, the relationship between male and female screw rotors with equal pitch and male and female screw rotors with variable pitch is defined in order to explain that by comparing under the approximately same conditions described above, the use of a screw rotor with variable pitch expands the range in which a fuel filler port can be installed, compared to the equal pitch screw rotors that have been used in conventional screw rotors for liquid feed systems.

[0032] Here, to define plane C, the helix angle is defined as the acute angle formed by the ridge line at a point on the tip of the screw rotor tooth and a plane parallel to the screw rotor end face. Point C is the point where the helix angle of the male screw rotor 23 with constant pitch and the helix angle of the male screw rotor 21 with variable pitch are equal. In addition, plane C is the plane that includes point C and is parallel to the screw rotor end face.

[0033] The action and effect of this embodiment will be explained using Fig. 6. Fig. 6(a) shows a male screw rotor 21 with variable pitch and a female screw rotor 22 with variable pitch of this embodiment, as viewed from direction B in Fig. 2. Fig. 6(b) shows a male screw rotor 23 with uniform pitch and a female screw rotor 24 with uniform pitch, as viewed from direction B in Fig. 2. Fig. 6 shows a screw rotor with a different rotation angle from that in Fig. 5.

[0034] Here, the volume of the working chamber is calculated by multiplying the axial length of the working chamber by the groove area of ​​the screw rotor cross section perpendicular to the axial direction of the screw rotor. Since the screw rotor in Figure 6(a) and the screw rotor in Figure 6(b) have the same cross-sectional shape perpendicular to the axial direction, if the axial lengths of the working chambers are the same, then the volumes of the working chambers will be the same.

[0035] 6(a) and 6(b) have the same axial length and volume, and therefore, assuming that the working chamber pressure is the same, when the same liquid supply mechanism is used and the liquid supply port is connected to the working chamber of either screw rotor specification, the same flow rate of liquid can be supplied to both working chamber 25 and working chamber 26. Here, the axial spacing of the lobe ridge lines forming working chamber 25 is wider than the axial spacing of the lobe ridge lines forming working chamber 26, and the area on the bore inner wall surface through which the liquid supply port can be connected is wider in working chamber 25 than in working chamber 26.

[0036] 15 shows a graph with the axial distance from the suction end of the working chamber on the horizontal axis and the pressure in the working chamber on the vertical axis for the working chamber pressure 41 of a screw rotor whose pitch increases from the suction end to the discharge end and the working chamber pressure 40 of a screw rotor with a constant pitch. Here, the axial distance from the suction end of the working chamber is the position on the male screw rotor shaft of the ridge line of the lobe ridge line that forms the working chamber on the suction end side.

[0037] In the latter half of the compression stroke (upper part of the graph), when comparing working chambers at the same pressure, it can be seen that the working chamber position is closer to the discharge end face in the screw rotor with variable pitch than in the screw rotor with constant pitch, and the liquid supply port can be installed in a range closer to the discharge end face.

[0038] In other words, as can be seen from the graph in Fig. 15, when the pitch of the screw rotor increases from the suction end face to the discharge end face, the range in which the liquid supply mechanism can be installed can be made wider by locating it on the discharge end face side compared to a screw rotor with an equal pitch. Here, the discharge end face side is the right side in Fig. 15.

[0039] In Figure 15, the position on the horizontal axis (distance from the suction end face of the working chamber) at the point where the line graph of a screw rotor with a constant pitch intersects with the line graph of a screw rotor whose pitch increases from the suction end face to the discharge end face corresponds to point C in Figure 5.

[0040] To the right of point C, that is, the range where the line graph of the screw rotor with equal pitch exceeds the line graph of the screw rotor whose pitch increases from the suction end face to the discharge end face in terms of working chamber pressure (vertical axis).

[0041] This range is the range in which the pressure in the working chamber at a certain position in a screw rotor whose pitch increases from the suction end face to the discharge end face and a screw rotor whose cross-sectional shape and dimensions perpendicular to the axial direction of the screw rotor, total wrap angle, and length are the same, and whose pitch is equally spaced, is higher than the pressure in the working chamber at the same position in a screw rotor whose pitch increases from the suction end face to the discharge end face. By arranging the liquid supply mechanism in such a range, the range in which the liquid supply mechanism can be installed can be expanded compared to the case where screw rotors with equal intervals are used.

[0042] By obtaining the data in Figure 15 through simulation or experiment, it is possible to obtain a method for determining the location of a liquid supply mechanism by comparing the pressure in the working chamber of a screw rotor whose pitch increases from the suction end face to the discharge end face with that of an equally spaced screw rotor that has the same cross-sectional shape and dimensions perpendicular to the rotor axial direction, the same total wrap angle, and length as the screw rotor and has an equally spaced pitch, and determining the range in which the pressure in the working chamber of the equally spaced screw rotor is higher than the pressure in the working chamber of a screw rotor whose pitch increases from the suction end face to the discharge end face, and then locating the liquid supply mechanism within that determined range.

[0043] According to the first embodiment, as shown in Fig. 6, the area on the bore inner wall surface where the liquid supply port can communicate with the working chamber 25 is wider than when the liquid supply port is communicated with the working chamber 26, is on the discharge end face side of the surface C of the male screw rotor 21 whose pitch changes and the female screw rotor 22 whose pitch changes. Therefore, if the liquid supply port can be provided on the discharge end face side of the surface C, the range in which the liquid supply port can be provided can be expanded.

[0044] Furthermore, within the range in which this liquid supply port can be installed, as shown in Figure 6, the distance between the liquid supply port 27a communicating with the working chamber 25 and the discharge port can be made shorter than the distance between the liquid supply port 27b communicating with the working chamber 26 and the discharge port, thereby shortening the distance the screw rotor transports the liquid and reducing stirring losses.

[0045] In this embodiment, a variable pitch screw rotor is used in which the pitch changes continuously and uniformly, but the pitch may change in stages, or the rate at which the pitch changes may change midway.

[0046] If there are multiple points where the helix angle of the screw rotor with variable pitch in this embodiment is the same as the helix angle of an assumed screw rotor with constant pitch, the point closest to the suction end face is designated as point C, and the liquid supply port is installed on the discharge end face side of a plane that includes point C and is parallel to the suction or discharge end face. Further, although a single liquid supply port is provided in this embodiment, a plurality of liquid supply ports may be provided. EXAMPLES

[0047] Example 2 will be described with reference to Figures 3, 7, 8, 9, and 10. Note that this example relates to a liquid feed screw compressor like Example 1, and the same parts as Example 1 will be described with the same reference numerals.

[0048] In this embodiment, the male screw rotor 2 and the female screw rotor 3 shown in Figure 3 are respectively a male screw rotor 21 with a variable pitch and a female screw rotor 22 with a variable pitch, and a jet collision nozzle 28 is installed on the discharge end face side of surface C as shown in Figure 7.

[0049] The jet impingement nozzle will be described with reference to Fig. 8. A cross-sectional view of the jet impingement nozzle is shown in Fig. 8. A first jet port 29 and a second jet port 30, each having a smaller diameter than the liquid supply port 14, are connected to the end of the liquid supply port 14 at an angle θ to each other, and the first jet port 29 and the second jet port 30 communicate with the working space 11.

[0050] The first injection port 29 and the second injection port 30 intersect on the working space 11 side, and the intersection point is located on the tooth groove of the screw rotor. The liquid flows from the liquid supply port 14 into the first injection port 29 and the second injection port 30, and the liquids injected from each of them collide with each other and then spread out.

[0051] Due to the diffusion of the liquid, the liquid spreads widely in the working chamber, achieving a high cooling effect. On the other hand, the jet impingement nozzle has a large pressure loss when supplying liquid, and the amount of liquid that can be supplied from a single jet impingement nozzle is smaller than that of a drilled hole. To ensure the amount of liquid to be supplied, it is necessary to increase the number of liquid supply ports, but the range in which the liquid supply ports can be installed is restricted by the pressure difference between the liquid supply source pressure and the pressure of the working chamber to which the liquid supply port is connected, and by the size of the compressor.

[0052] This embodiment can expand the range in which the liquid supply ports can be installed, and can achieve the effect of reducing the mixing loss, as in the case of embodiment 1. In addition, by expanding the range in which the liquid supply ports can be installed, it becomes possible to install more liquid supply ports than before, and a sufficient amount of liquid can be supplied even when a jet impingement nozzle is used.

[0053] Furthermore, in a screw compressor using a male screw rotor 21 with variable pitch and a female screw rotor 22 with variable pitch, the distance between the lobe crest lines forming any working chamber on the discharge end face side of face C is wider than in the case of using a male screw rotor 23 with a uniform pitch and a female screw rotor 24 with a uniform pitch, so that the liquid supplied from the fine liquid supply port is diffused over a wide area, resulting in a higher cooling effect.

[0054] The same effect can be obtained by any liquid supply mechanism or fine liquid supply mechanism that spreads the liquid over a wide area, including a fan spray nozzle as exemplified in FIG. 10, other than the jet impingement nozzle.

[0055] The fan spray nozzle will be described with reference to a cross-sectional view in Fig. 9. Liquid that flows into the liquid supply port 14 flows into the working space 11 through the slit portion 31. Fig. 10 shows the connection between the slit portion 31 and the working space 11. The slit portion 31 has a shape in which the longitudinal dimension a of the slit is longer than the width dimension b.

[0056] The liquid injected from the slit portion 31 into the working space 11 spreads more widely in the direction of dimension a (the longitudinal direction of the slit) than in the direction of dimension b (the width direction of the slit). The liquid is injected from the slit portion 31 in the form of a film, and then breaks down into atomized particles.

[0057] In this embodiment, one fine particle supply port such as a jet impingement nozzle or a fan spray nozzle is provided, but multiple supply ports may be provided in the axial direction of the screw rotor, that is, at least one fine particle supply port and at least one drilled hole supply port may be provided in one compressor. For example, in a small compressor, if the space for installing multiple fine particle supply ports cannot be secured, a drilled hole supply port is provided on the suction end face side and a fine particle supply port is provided on the discharge end face side, thereby obtaining a high cooling effect of the fine particle supply while securing the amount of liquid required for lubricating the screw rotor. EXAMPLES

[0058] The configuration of this embodiment will be described with reference to Figures 2, 3, 11, 13, and 16. Furthermore, the same parts as those described above will be denoted by the same reference numerals.

[0059] In this embodiment, the male screw rotor 2 and female screw rotor 3 shown in Figure 3 are respectively a male screw rotor 32 with variable pitch and a female screw rotor 33 with variable pitch shown in Figure 13, and a drilled hole liquid supply port 27 is provided on the suction end face side rather than plane D shown in Figure 13.

[0060] The variable-pitch male screw rotor 32 and the variable-pitch female screw rotor 33 are screw rotors whose pitch decreases from the suction end face toward the discharge end face.

[0061] Figure 11(a) shows a male screw rotor 32 with a variable pitch and a female screw rotor 33 with a variable pitch, viewed from direction B in Figure 2, with the upper side of Figure 11 being the suction end surface and the lower side being the discharge end surface.

[0062] Figure 11(b) shows an equal-pitch male screw rotor 34 and an equal-pitch female screw rotor 35 as viewed from direction B in Figure 2. However, the equal-pitch male screw rotor 34 is defined as a screw rotor whose pitch does not change from the suction end face to the discharge end face, and which is equal to the male screw rotor 32 whose pitch changes in terms of the shape and dimensions of the cross section perpendicular to the screw rotor axis, the screw rotor length, and the total wrap angle.

[0063] The equal-pitch female screw rotor 35 is defined as a screw rotor whose pitch does not change from the suction end face to the discharge end face, and which is equal to the variable-pitch female screw rotor 33 in terms of the shape and dimensions of the cross section perpendicular to the screw rotor axis, the screw rotor length, and the total wrap angle.

[0064] In addition, the point where the helix angle of the male screw rotor 34 with constant pitch and the helix angle of the male screw rotor 32 with variable pitch are equal is defined as point D, and the plane that includes point D and is parallel to the end face of the screw rotor is defined as plane D.

[0065] The action and effect of this embodiment will be described with reference to Figure 12. Figure 12(a) shows a male screw rotor 32 with a variable pitch and a female screw rotor 33 with a variable pitch, as viewed from direction B in Figure 2. Figure 12(b) shows a male screw rotor 34 with a uniform pitch and a female screw rotor 35 with a uniform pitch, as viewed from direction B in Figure 2. Figure 12 shows a screw rotor with a different rotation angle from that in Figure 11.

[0066] Since the working chambers 36 and 37 have the same volume, assuming the same pressure, regardless of which working chamber the liquid supply port is connected to, when the same liquid supply mechanism is used, the same flow rate of liquid can be supplied to both the working chambers 36 and 37.

[0067] Here, the axial spacing of the lobe ridge lines forming working chamber 36 is wider than the axial spacing of the lobe ridge lines forming working chamber 37, so the area on the bore inner wall surface that can communicate with the liquid supply port is wider in working chamber 36 than in working chamber 37.

[0068] FIG. 16 shows a graph of the working chamber pressure 42 of a screw rotor whose pitch decreases from the suction end face to the discharge end face, and the working chamber pressure 40 of a screw rotor with a constant pitch, with the horizontal axis representing the axial distance from the suction end face of the working chamber and the vertical axis representing the working chamber pressure.

[0069] Here, the axial distance from the suction end face of the working chamber is the position on the screw rotor axis of the lobe crest line on the suction end face side of the working chamber. From this graph, it can be seen that in the first half of the compression stroke (lower part of the graph), when comparing working chambers at the same pressure, the screw rotor with variable pitch has the working chamber position closer to the discharge end face than the screw rotor with constant pitch, and the liquid supply port can be installed in a range closer to the discharge end face.

[0070] In other words, as can be seen from the graph in Fig. 16, when the pitch of the screw rotor decreases from the suction end face to the discharge end face, the possible installation range can be made wider by locating the liquid supply mechanism on the suction end face side compared to a screw rotor with a uniform pitch. Here, the suction end face side is the left side in Fig. 16.

[0071] In Figure 16, the position on the horizontal axis (distance from the suction end face of the working chamber) at the point where the line graph of a screw rotor with a constant pitch intersects with the line graph of a screw rotor whose pitch increases from the suction end face to the discharge end face corresponds to point D in Figure 11.

[0072] To the left of point D, that is, the range where the line graph of the screw rotor with a constant pitch exceeds the line graph of the screw rotor whose pitch decreases from the suction end face to the discharge end face in terms of working chamber pressure (vertical axis).

[0073] This range is the range in which the pressure in the working chamber at a certain position in a screw rotor whose pitch decreases from the suction end face to the discharge end face and a screw rotor whose cross-sectional shape and dimensions perpendicular to the axial direction of the screw rotor, total winding angle, and screw rotor length are the same and whose pitch is equal, is higher than the pressure in the working chamber at the same position in a screw rotor whose pitch decreases from the suction end face to the discharge end face. If the liquid supply mechanism is located in such a range, the range in which the liquid supply mechanism can be installed can be expanded compared to the case where a screw rotor with equal pitches is used.

[0074] By obtaining the data in Figure 16 through simulation or experiment, it is possible to obtain a method for determining the location of a liquid supply mechanism by comparing the pressure in the working chamber of a screw rotor with an equally spaced pitch and having the same cross-sectional shape and dimensions perpendicular to the rotor axial direction as the screw rotor, the same total wrap angle, and length, and determining the range in which the pressure in the working chamber of the equally spaced screw rotor is higher than the pressure in the working chamber of a screw rotor with a smaller pitch from the suction end face to the discharge end face, and then locating the liquid supply mechanism within that determined range.

[0075] 12, in the third embodiment, the area on the bore inner wall surface where the liquid supply port can communicate with working chamber 36 is wider than when it communicates with working chamber 37, is on the suction end face side of plane D. Therefore, when the liquid supply port is provided on the suction end face side of plane D, the area in which the liquid supply port can be provided can be expanded.

[0076] Furthermore, within the range in which this liquid supply port can be installed, the distance between the oil supply port communicating with the working chamber 36 and the discharge port can be made shorter than the distance between the oil supply port communicating with the working chamber 37 and the discharge port, as shown by the arrow in Figure 12. This shortens the distance the screw rotor transports the liquid, and reduces the stirring loss.

[0077] Although a single liquid supply port is provided in this embodiment, a plurality of liquid supply ports may be provided. In the case where there are multiple points where the helix angle of the screw rotor with variable pitch in this embodiment is the same as the helix angle of an assumed screw rotor with constant pitch, the point closest to the suction end face is designated as point D, and the liquid supply port is installed on the suction end face side of a plane that includes point D and is parallel to the suction or discharge end face. EXAMPLES

[0078] The present embodiment will be described with reference to Fig. 14. Note that the present embodiment relates to a liquid supply type screw compressor like the third embodiment, and the same parts as the third embodiment will be described with the same reference numerals.

[0079] In this embodiment, the male screw rotor 2 and the female screw rotor 3 shown in Fig. 3 are respectively a male screw rotor 32 with a variable pitch and a female screw rotor 33 with a variable pitch shown in Fig. 14. The jet collision nozzle 28 is installed closer to the suction end face than plane D in Fig. 14.

[0080] The jet collision nozzle, which is one of the fine particle supply mechanisms used in this embodiment, has a large pressure loss when supplying liquid, and when the pressure difference between the working chamber pressure to which the liquid supply port is connected and the liquid supply source pressure is the same, the amount of liquid supplied is less than when supplying liquid using a drilled hole.

[0081] In the screw compressor using the variable pitch male screw rotor 32 and variable pitch female screw rotor 33 of this embodiment, the area where the working chamber pressure is lower can be expanded on the suction end face side of surface D compared to the uniform pitch male screw rotor 34 and the uniform pitch female screw rotor 35.

[0082] In other words, the area where the difference between the liquid supply source pressure and the working chamber pressure where the liquid supply port is connected can be expanded. This not only reduces the mixing loss as in the third embodiment, but also ensures a sufficient amount of liquid supply by the jet impingement nozzle, resulting in a high cooling effect.

[0083] The same effect can be obtained by any liquid supply mechanism or fine liquid supply mechanism that spreads the liquid over a wide area, including a fan spray nozzle as exemplified in FIG. 10, other than the jet impingement nozzle.

[0084] In this embodiment, a single fine particle liquid supply port is provided, but multiple liquid supply ports may be provided, or multiple drilled hole liquid supply ports may be provided, or multiple liquid supply ports may be provided by combining a drilled hole liquid supply port and a fine particle liquid supply port. [Explanation of symbols]

[0085] 1...Screw compressor, 4...Casing, 21...32...Male screw rotor with variable pitch, 22...33...Female screw rotor with variable pitch, 27...Liquid supply port

Claims

1. A screw rotor; A casing that houses the screw rotor; a liquid supply mechanism for supplying liquid to a working chamber surrounded by the casing, and the screw rotor is A screw compressor characterized in that the pitch increases monotonically in the axial direction from the suction end face to the discharge end face.

2. 2. The screw compressor according to claim 1, The screw rotor has the same cross-sectional shape and dimensions perpendicular to the axial direction of the screw rotor, the same total wrap angle, and the same length, and the same pitch. The pressure in the working chamber communicates with a liquid supply port provided at a certain position on the inner wall of the bore of the screw rotor. a liquid supply mechanism disposed at a position where the pressure is higher than the pressure in the working chamber communicated with a liquid supply port provided at the same position of the screw rotor;

3. 2. The screw compressor according to claim 1, The helix angle of the screw rotor is equal to the helix angle of a screw rotor having the same shape and size of the screw rotor and a cross section perpendicular to the axial direction of the screw rotor, the same full wrap angle, and the same length, and having an equal pitch; and wherein the liquid supply mechanism is disposed closer to the discharge end face than a plane parallel to the suction end face and the discharge end face.

4. 4. The screw compressor according to claim 1, wherein the liquid supply mechanism includes a fine particle liquid supply port.

5. 5. The screw compressor according to claim 1, further comprising a plurality of liquid supply ports arranged in an axial direction of the screw rotor.

6. The screw compressor according to any one of claims 1 to 5, The screw compressor is characterized in that the liquid supply mechanism has at least one fine particle liquid supply port and at least one drilled hole liquid supply port.

7. 7. The screw compressor according to claim 1, wherein the liquid supply mechanism comprises a jet impingement nozzle or a fan spray nozzle.

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