Oil-free screw compressor

Abstract

To shorten a discharge side rotor shaft of an oil-free screw compressor as much as possible.SOLUTION: An axial length of a bearing 44 supporting a discharge side rotor shaft 32 of a second (female) screw rotor 0 is formed short compared to a bearing 42 supporting a discharge side rotor shaft 22 of a first (male) screw rotor. Further, a distance Lcf from a discharge side end surface 30a of the second screw rotor to a timing gear 52 side surface of a second pressing plate 18 is set short compared to a distance Lcm from a discharge side end surface 20a of the first screw rotor 20 to a timing gear 51 side surface of a first pressing plate 17. The structure makes a distance Wf between the second pressing plate 18 and a second timing gear 52 wider than a thickness Tf of a head of a fixing bolt 19b which fixes the second pressing plate 18.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an oil-free screw compressor, and more particularly to an oil-free screw compressor characterized by a bearing mounting structure on the discharge side of the oil-free screw compressor. [Background technology]

[0002] As shown in Figure 5, the oil-free screw compressor 100 compresses the gas to be compressed by rotating a pair of male and female screw rotors 120, 130 in a non-contact state within a rotor chamber 111 formed within a cylinder 110, and is configured so that the gas to be compressed can be compressed without introducing lubricating oil for cooling, lubrication, and sealing into the compression working space defined by the inner wall of the rotor chamber 111 and the screw rotors 120, 130.

[0003] Therefore, since the oil-free screw compressor 100 produces compressed gas that does not contain oil, it is widely used in fields that require clean compressed gas, such as the medical field, papermaking, chemistry, and food manufacturing.

[0004] The screw rotors 120, 130 of this oil-free screw compressor 100 have rotor shafts 121, 122; 131, 132 protruding from the suction side and discharge side, respectively, and these rotor shafts 121, 122; 131, 132 are supported by bearings 141, 142; 143, 144 provided in shaft holes 115, 116; 112, 113, respectively, so that the screw rotors 120, 130 are rotatably accommodated within the rotor chamber 110.

[0005] In order to rotate the pair of male and female screw rotors 120, 130 without contact, timing gears 151, 152 are attached to the discharge side rotor shafts 122, 132 of the screw rotors 120, 130, respectively, and the two timing gears 151, 152 are meshed together.The suction side rotor shaft 121 of the male screw rotor 120 is protruded outside the machine through a shaft hole 115 that penetrates the inlet casing 114 that closes the suction side end of the cylinder 110, and serves as a drive shaft.By inputting rotational driving force from a drive source such as an engine or motor (not shown) to this drive shaft, the screw rotors 120, 130 can be meshed and rotated without contact.

[0006] In such an oil-free compressor 100, thrust loads can be supported by angular bearings 142b and 144b, and radial loads can be supported by cylindrical roller bearings 141, 142a, 143 and 144a, respectively. The angular bearings 142b and 144b that support thrust loads are provided only on the discharge side rotor shafts 122 and 132, while the cylindrical roller bearings 141, 142a, 143 and 144a that support radial loads are provided on both the discharge side and the suction side rotor shafts 121, 122; 131 and 132.

[0007] In addition, spacer rings 142c, 144c with oil supply holes for jet oil supply are provided between the angular bearings 142b, 144b and the cylindrical roller bearings 142a, 144a on the discharge side bearings 142, 144, and air seals 161, 162 are provided between the bearings 142, 144 and the rotor chamber 111 to prevent the compressor body in the rotor chamber 111 from leaking toward the bearings 142, 144, and oil seals 163, 164 are provided between the bearings 142, 144 and the rotor chamber 111 to prevent the lubricating oil supplied to the bearings 142, 144 from seeping into the rotor chamber 111.

[0008] As shown in FIG. 6, shaft holes 112, 113 into which the discharge-side rotor shafts 122, 132 are inserted are provided in the cylinder 110, and the aforementioned air seals 161, 162, oil seals 163, 164, cylindrical roller bearings 142a, 144a, spacer rings 142c, 144c, and angular bearings 142b, 144b are arranged in the gaps formed between the inner walls of the shaft holes 112, 113 and the outer peripheries of the discharge-side rotor shafts 122, 132 inserted into the shaft holes 112, 113. In this state, pressure plates 117, 118 are attached to the discharge side end 110a of the cylinder 110 with fixing bolts 119a, 119b so as to cover the peripheral portions of the opening ends 112a, 113a of the shaft holes 112, 113, and these pressure plates 117, 118 fix the outer rings of the angular bearings 142b, 144b so as not to fall out of the shaft holes 112, 113, thereby attaching these components to the shaft holes 112, 113 (see Patent Document 1). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Microfilm of Utility Model Application No. 63-153628 (Utility Model Application No. 2-74592) Summary of the Invention [Problem to be solved by the invention]

[0010] In the oil-free screw compressor 100 having the above-described configuration, the male screw rotor 120 side to which the rotational driving force is input from the driving source requires relatively high strength, so the rotor shafts 121, 122 of the male screw rotor 120 are formed thicker than the rotor shafts 131, 132 of the female screw rotor 130, and also for the bearings 141, 142; 143, 144, the bearings 141, 142 on the male screw rotor 120 side are larger than the bearings 143, 144 on the female screw rotor 130 side.

[0011] Thus, on the female screw rotor 130 side where the small bearing 144 is adopted as compared with the bearing 142 on the male screw rotor 120 side, the overall length of the bearing 144 in the axial direction of the discharge side rotor shaft 132 becomes shorter as compared with the bearing 142 provided on the male screw rotor 120 side.

[0012] Therefore, the distance Laf from the discharge side end face 130a of the female screw rotor 130 to the outboard end face of the angular bearing 144b provided in the female bearing 144 becomes shorter as compared with the distance Lam from the discharge side end face 120a of the male screw rotor 120 to the outboard end face of the angular bearing 142b provided in the male bearing 142 [Laf < Lam: refer to Fig. 6(A)].

[0013] However, in the oil-free screw compressor 100, as described above, in order to rotate the male screw rotor 120 and the female screw rotor 130 in a non-contact manner, timing gears 151 and 152 that mesh and rotate with each other are attached to the discharge side rotor shaft 122 of the male screw rotor 120 and the discharge side rotor shaft 132 of the female screw rotor 130. Therefore, the distance Lb from the discharge side end faces 120a and 130a of both screw rotors 120 and 130 to the center in the thickness direction of the timing gears 151 and 152 needs to be a common length on the male side and the female side to ensure the meshing of the timing gears 151 and 152.

[0014] Therefore, in the conventional oil-free screw compressor 100, the bearings 142, 144 are attached to the discharge-side shaft holes 112, 113 as shown in Figure 6(A), by inserting the bearing 142 into the shaft hole 112 on the male side so that the outboard end face of the outer ring of the angular bearing 142b protrudes slightly outboard beyond the opening end 112a of the shaft hole 112, and fixing the outer ring of the angular bearing 142b with a pressure plate 117, while on the female side, the bearing 144 is attached so that the outboard end face of the angular bearing 144b is recessed toward the rotor chamber 111 beyond the opening end 113a of the shaft hole 113, and the outer ring of the angular bearing 144b is fixed in a pressed state toward the rotor chamber 111 with a cylindrical spacer 118a (the part colored gray in Figure 6(A)) provided integrally with or separately from the pressure plate 118, thereby fixing the bearing 144 within the shaft hole 113.

[0015] By configuring in this manner, the pressure plates 117, 118 are attached to the discharge side end 110a of the cylinder 110 so that the sides of the timing gears 151, 152 of both the male and female pressure plates 117, 118 are arranged on the same plane, and the distance Lc from the discharge side end faces 120a, 130a of the screw rotors 120, 130 to the sides of the pressure plates 117, 118 on the timing gears 151, 152 side is configured to be the same length on both the female side and the male side.

[0016] Furthermore, as shown in the cross section in Figure 7, the number of grooves on the female screw rotor 130, which is the driven side (six in the illustrated example), is greater than the number of teeth on the male screw rotor 120, which is the driving side (four in the illustrated example), so that the rotational speed of the female screw rotor 130 is slower than that of the male screw rotor 120.

[0017] Therefore, the timing gear 152 attached to the discharge side rotor shaft 132 of the female screw rotor 130 has a larger outer diameter than the timing gear 151 attached to the discharge side rotor shaft 122 of the male screw rotor 120.

[0018] On the other hand, the discharge side rotor shaft 122 of the male screw rotor 120 on the driving side is thicker than that of the female screw rotor 130 and is supported by a large bearing 142, so the shaft hole 112 is correspondingly larger and the fixing bolt 119a that fixes the pressure plate 117 is screwed into the cylinder 110 at a position away from the axis of the discharge side rotor shaft 122 provided on the male screw rotor 120.

[0019] As a result, the head of the fixing bolt 119a of the pressure plate 117 on the male screw rotor 120 side is positioned outside the outer diameter circle of the timing gear 151 as shown in FIG. 6(B).

[0020] According to this positional relationship between the timing gear 151 and the fixing bolt 119a on the male screw rotor 120 side, even if the distance Wm between the timing gear 151 and the pressure plate 117 is set to be less than the thickness Tm of the head of the fixing bolt 119a, interference between the timing gear 151 and the head of the fixing bolt 119a can be avoided.

[0021] However, the discharge side rotor shaft 132 provided on the female screw rotor 130 side is thin, and the bearing 144 that supports it is also small, so on the female side, the fixing bolt 119b is positioned relatively close to the axis of the discharge side rotor shaft 132, and the timing gear 152 provided on the female screw rotor 130 has a larger diameter than the timing gear 151 provided on the male screw rotor 120.

[0022] Therefore, on the female screw rotor side, a part of the head of the fixing bolt 119b is disposed inside the outer diameter circle of the timing gear 152 as shown in FIG. 6(B).

[0023] Due to this positional relationship between the timing gear 152 and the fixing bolt 119b, on the female screw rotor 130 side, in order to avoid interference between the timing gear 152 and the head of the fixing bolt 119b, it is necessary to make the distance Wf between the timing gear 152 and the pressure plate 118 wider than the thickness Tf of the head of the fixing bolt 119b.

[0024] Therefore, in order to ensure meshing of the two timing gears 151, 152, it is necessary to make the spacing Wm between the timing gear 151 and the pressure plate 117 on the male screw rotor 120 side relatively wide to correspond to the spacing Wf used on the female side.

[0025] In this way, in the conventional oil-free screw compressor 100, the distance Lc from the discharge side end faces 120a, 130a of the screw rotors 120, 130 to the timing gear side side of the pressure plates 117, 118 was made long to correspond to the configuration of the male screw rotor 120 side, and the spacing Wm, Wf between the pressure plates 117, 118 and the timing gears 151, 152 was made wide to correspond to the configuration of the female screw rotor 130 side, and both were adjusted to suit the longer / wider side, resulting in long overall lengths for both the male and female discharge side rotor shafts 122, 132.

[0026] In this way, if the overall length of the discharge side rotor shafts 122, 132 is increased, the moment load on the cylindrical roller bearings 142a, 144a by the timing gears 151, 152 will increase, which will reduce the life of the cylindrical roller bearings 142a, 144a, and cause the reliability of the oil-free screw compressor to decrease.

[0027] Furthermore, as mentioned above, if the distance Lc from the discharge side end faces 120a, 130a of the screw rotors 120, 130 to the end faces of the pressure plates 117, 118 on the timing gear 151, 152 side becomes longer, it becomes necessary to form correspondingly longer axial holes 112, 113 in the cylinder 110, which not only increases the size of the cylinder 110 but also reduces the workability of the axial holes 112, 113 in the cylinder 110.

[0028] In particular, in the oil-free screw compressor 100, lubricating oil is not supplied to the compression working space for lubrication, cooling, and sealing, so the sealing of the compression working space is poorer than in an oil-cooled screw compressor, and the amount of compressed gas that leaks out is also greater.To compensate for this, the screw rotors 120, 130 are rotated at high speed to generate compressed gas.

[0029] Therefore, in the oil-free screw compressor 100, the bearings 141 to 144 are employed in sizes as small as possible so that the centrifugal force acting on the rolling elements of the bearings 141 to 144 is reduced.

[0030] By adopting such small bearings 142, 144, the axial holes 112, 113 formed in the cylinder 110 also become smaller, making it difficult to install and visually inspect parts that are installed in recessed positions in the axial holes 112, 113, such as air seals 161, 162 and oil seals 163, 164.

[0031] Therefore, the present invention has been made to eliminate the drawbacks of the above-mentioned conventional technology, and aims to provide an oil-free screw compressor that has a relatively simple configuration, yet can shorten the length of the discharge side rotor shaft of the oil-free screw compressor as much as possible while ensuring engagement of the timing gear and avoiding interference between the head of the fixing bolt and the timing gear, thereby reducing the moment load and improving the life of the cylindrical roller bearings, thereby increasing reliability, and by shortening the overall length of the shaft hole formed in the cylinder, makes it possible to make the cylinder smaller and lighter, and also makes it easy to attach and detach parts such as air seals and oil seals that are attached in recessed positions within the shaft hole, and to visually inspect them. [Means for solving the problem]

[0032] The means for solving the problems are described below together with the reference numerals used in the description of the embodiment of the invention. These reference numerals are intended to clarify the correspondence between the claims and the description of the embodiment of the invention, and needless to say, are not used to restrict the interpretation of the technical scope of the present invention.

[0033] Furthermore, in this specification, the terms "first" and "second" are used only to distinguish between components or elements, and these terms do not have the meaning of ordinal numbers that define rank, order, etc.

[0034] In order to achieve the above object, the oil-free screw compressor 1 of the present invention is a cylinder 10 provided with a rotor chamber 11 for rotatably accommodating a first screw rotor 20, which is either a male or female screw rotor (a male screw rotor in the illustrated example), and a second screw rotor 30, which is the other screw rotor (a female screw rotor in the illustrated example), and also provided with a first shaft hole 12 into which a discharge side rotor shaft 22 of the first screw rotor 20 is inserted, and a second shaft hole 13 into which a discharge side rotor shaft 32 of the second screw rotor is inserted; a first bearing 42 attached to the first shaft hole 12 and supporting the discharge side rotor shaft 22 of the first screw rotor 20, and a second bearing 44 attached to the second shaft hole 13 and supporting the discharge side rotor shaft 32 of the second screw rotor 30; a first pressing plate 17 that fixes the first bearing 42, and a second pressing plate 18 that fixes the second bearing 44, which are attached to the discharge side end 10a of the cylinder 10, where the first and second shaft holes 12, 13 open, via fixing bolts 19a, 19b, respectively; The pump is provided with a first timing gear 51 attached to the discharge side rotor shaft 22 of the first screw rotor 20 passing through the first pressure plate 17, and a second timing gear 52 attached to the discharge side rotor shaft 32 of the second screw rotor 30 passing through the second pressure plate 18, In an oil-free screw compressor in which the axial length of the second bearing 44 is formed shorter than that of the first bearing 42, and at least a portion of the fixing bolt 19b that fixes the second pressing plate 18 is arranged inside the outer diameter circle of the second timing gear 52, The first and second bearings 42, 44 are accommodated in the first and second shaft holes 12, 13 so that portions of the first and second bearings 42, 44 protrude from the opening ends 12a, 13a of the first and second shaft holes 12, 13, and the ends of the first and second bearings 42, 44 protruding from the first and second shaft holes 12, 13 are fixed by the cylinder side sides of the first and second pressing plates 17, 18 attached to the discharge side end 10a of the cylinder 10, with gaps δm, δf being generated between the opening ends 12a, 13a of the first and second shaft holes 12, 13, The distance Lcf from the discharge side end face 30a of the second screw rotor 30 to the side face of the second pressing plate 18 on the second timing gear 52 side is shorter than the distance Lcm from the discharge side end face 20a of the first screw rotor 20 to the side face of the first pressing plate 17 on the first timing gear 51 side, so that the spacing Wf between the second pressing plate 18 and the second timing gear 52 is wider than the thickness Tf of the head of the fixing bolt 19b that fixes the second pressing plate 18 (Claim 1; see Figures 2 to 4).

[0035] In the oil-free screw compressor 1 having the above configuration, when the fixing bolt 19a that fixes the first pressing plate 17 is arranged outside the outer diameter circle of the first timing gear 51, It is preferable that the distance Wm between the first pressure plate 17 and the first timing gear 51 is narrower than the thickness Tm of the head of the fixing bolt 19a that fixes the first pressure plate 17 (Claim 2; see Figures 2 to 4).

[0036] In addition, in the oil-free screw compressor 1 having the above configuration, The first and second bearings 42, 44 respectively include cylindrical roller bearings 42a, 44a arranged on the rotor chamber 11 side and angular bearings 42b, 44b arranged on the outer side of the cylindrical roller bearings 42a, 44a, The first and second bearings 42, 44 are accommodated in the first and second shaft holes 12, 13 so that portions of the angular bearings 42b, 44b provided in the first and second bearings 42, 44 protrude from the opening ends 12a, 13a of the first and second shaft holes 12, 13. Rumo (Claim 3; see Figures 2 and 3).

[0037] When providing such gaps δm and δf, the gap δm between the first pressure plate 17 and the opening end 12a of the first pressure plate 12 and the gap δf between the second pressure plate 18 and the opening end 13a of the second pressure plate 13 may be made to have the same width, for example by providing a bulge 10b on the first (male) screw rotor 20 side, where the periphery of the opening end 12a of the first shaft hole 12, including the attachment position of the fixing bolt 19a, bulges out toward the first timing gear 51, and / or by providing a recessed portion on the second (female) screw rotor 30 side, where the periphery of the opening end 13a of the second shaft hole 13, including the attachment position of the fixing bolt 19b, is recessed toward the rotor chamber 11 (claim 4; see Figures 3 and 4).

[0038] As mentioned above, in a configuration in which the gaps δm and δf between the first and second pressure plates 17, 18 and the opening ends 12a, 13a of the first and second axial holes 12, 13 are the same, the fixing bolt 19a used to fix the first pressure plate 17 and the fixing bolt 19b used to fix the second pressure plate 18 may be bolts of the same dimensions (Claim 5; see Figures 3 and 4). [Effects of the Invention]

[0039] With the configuration of the present invention described above, the oil-free screw compressor 1 of the present invention can achieve the following significant effects.

[0040] By making the distance Lcf from the discharge side end face 30a of the second (female) screw rotor 30 to the side of the second pressure plate 18 on the second timing gear 52 side shorter than the distance Lcm from the discharge side end face 20a of the first (male) screw rotor 20 to the side of the first pressure plate 17 on the first timing gear 51 side, it is possible to ensure that the spacing Wf between the second pressure plate 18 and the second timing gear 52 is greater than the thickness Tf of the head of the fixing bolt 19b, and the lengths of both the first and second discharge side rotor shafts 22, 32 can be shortened.

[0041] In particular, when the fixing bolt 19a that fixes the first pressure plate 17 is positioned outside the outer diameter circle of the first timing gear 51, the length of the discharge side rotor shafts 22, 32 of the first and second screw rotors 20, 30 can be further shortened by configuring the spacing Wm between the first pressure plate 17 and the first timing gear 51 to be narrower than the thickness Tm of the head of the fixing bolt 19a.

[0042] As a result, the moment load applied to the cylindrical roller bearings 42a, 44a can be reduced, thereby increasing the lifespan of the cylindrical roller bearings 42a, 44a, and improving the reliability of the bearings 42, 44 and ultimately the oil-free screw compressor 1.

[0043] In both the first and second bearings 42, 44, a portion of the angular bearings 42b, 44b is positioned to protrude from the opening ends 12a, 13a of the first and second shaft holes 12, 13, and gaps δm, δf are provided between the first and second pressure plates 17, 18 and the opening ends 12a, 13a of the first and second shaft holes 12, 13, respectively. This configuration allows the overall length of the first and second shaft holes 12, 13 formed in the cylinder 10 to be shortened, improving the workability of the shaft holes 12, 13. In addition, the distance from the opening ends 12a, 13a of the first and second shaft holes 12, 13 to the oil seals 63, 64 and air seals 61, 62 is shortened, making it easier to install and visually inspect the oil seals 63, 64 and air seals 61, 62.

[0044] Furthermore, by shortening the overall length of the first and second axial holes 12, 13, it is possible to shorten the overall axial length of the cylinder 10, making it possible to make the cylinder 10 smaller and lighter.

[0045] Furthermore, if the gap δm between the first pressure plate 17 and the opening end 12a of the first shaft hole 12 and the gap δf between the second pressure plate 18 and the opening end 13a of the second shaft hole 13 are formed with different widths (see Figure 2(A)), then unless a fixing bolt that is longer is used to fix the wider side of the gaps δm, δf compared to the narrower side, there will be a difference in the threading length of the fixing bolts 19a, 19b into the screw holes provided in the cylinder 10, resulting in a difference in the attachment strength between the first pressure plate 17 and the second pressure plate 18.

[0046] However, in a configuration in which the gap δm between the first clamping plate 17 and the opening end 12a of the first axial hole 12 and the gap δf between the second clamping plate 18 and the opening end 13a of the second axial hole 13 are the same width (see Figures 3(A) and 4(A)), even if the same dimensions are used for the fixing bolts 19a, 19b of both the first and second clamping plates 17, 18, the threaded lengths of the fixing bolts 19a, 19b can be the same.

[0047] As a result, it became possible to use commonly designed fixing bolts to secure the first and second pressure plates 17, 18, which facilitated assembly work, improved productivity, and reduced costs by sharing parts. [Brief explanation of the drawings]

[0048] [Figure 1] 1 is a cross-sectional plan view of an oil-free screw compressor according to the present invention. [Figure 2] (A) is an enlarged view of a portion of Figure 1, and (B) is a view of (A) from the direction of arrow B. [Figure 3] 2(A) is a partially enlarged view of FIG. 1 showing a modification of FIG. 2(A), and FIG. 2(B) is a view of FIG. 2(A) as seen from the direction of arrow B. [Figure 4] 2(A) is a partially enlarged view of FIG. 1 showing yet another modified example of FIG. 2(A), and FIG. 2(B) is a view of FIG. 2(A) as seen from the direction of the arrow B. FIG. [Figure 5] FIG. 1 is a cross-sectional plan view of a conventional oil-free screw compressor. [Figure 6] (A) is an enlarged view of a portion of Figure 5, and (B) is a view of (A) from the direction of arrow B. [Figure 7] FIG. 2 is an explanatory diagram of the cross-sectional shapes of the male rotor and female rotor. DETAILED DESCRIPTION OF THE INVENTION

[0049] The configuration of the oil-free screw compressor of the present invention will be described below with reference to the accompanying drawings.

[0050] In the following embodiment, a configuration will be described in which the male screw rotor is the first screw rotor 20 and the female screw rotor is the second screw rotor 30, but the present invention may also be implemented in the opposite manner to this embodiment, with the female screw rotor being the first screw rotor and the male screw rotor being the second screw rotor.

[0051] In Figure 1, the symbol 1 denotes an oil-free screw compressor of the present invention, and a rotor chamber 11 is formed in the cylinder 10 of this oil-free screw compressor 1 to rotatably accommodate a pair of male and female screw rotors, and within this rotor chamber 11, the male screw rotor (first screw rotor) 20 and the female screw rotor (second screw rotor) 30 are configured to rotate in a non-contact manner while meshing with each other, thereby compressing the gas to be compressed.

[0052] Rotor shafts 21, 22, 31, 32, which are rotating shafts, are protrudingly formed at both ends of the first (male) and second (female) screw rotors 20, 30, respectively, and the inlet casing 14 attached to the suction side end face of the rotor chamber 10 is provided with shaft holes 15, 16 into which the suction side rotor shafts 21, 31 are inserted, and bearings (cylindrical roller bearings) 41, 43 that support the suction side rotor shafts 21, 31 inserted into the shaft holes 15, 16.

[0053] On the other hand, in the part of the cylinder 10 located on the discharge side relative to the rotor chamber 11, a first shaft hole 12 into which the discharge side rotor shaft 22 of the first screw rotor 20 is inserted, and a second shaft hole 13 into which the discharge side rotor shaft 32 of the second screw rotor 30 is inserted are formed, and first and second bearings 42, 44 equipped with cylindrical roller bearings 42a, 44a and angular bearings 42b, 44b are provided, respectively, to support the discharge side rotor shafts 22, 32 inserted into the first and second shaft holes 12, 13.

[0054] In order to allow the first and second screw rotors 20, 30 to mesh and rotate without contacting each other, a first timing gear 51 is attached to the discharge side rotor shaft 22 of the first screw rotor 20, and a second timing gear 52 is attached to the discharge side rotor shaft 32 of the second screw rotor 30.The two timing gears 51, 52 are meshed together, and the suction side rotor shaft 21 of one of the screw rotors 20 penetrates the inlet casing 14 and protrudes outside the machine to serve as a drive shaft.By inputting rotational driving force from a drive source such as an engine or motor (not shown) into this drive shaft, the screw rotors 20, 30 can rotate.

[0055] In addition, the first and second bearings 42, 44 provided on the discharge side are provided with spacer rings 42c, 44c with oil supply holes for jet oil supply between the angular bearings 42b, 44b and the cylindrical roller bearings 42a, 44a, similar to the oil-free screw compressor 100 described with reference to Figure 6, and air seals 61, 62 are provided between the first and second bearings 42, 44 and the rotor chamber 11, respectively, to prevent the compressed gas in the rotor chamber 11 from leaking toward the bearings 42, 44, and oil seals 63, 64 are provided between the first and second bearings 42, 44 and the rotor chamber 11, to prevent the compressed gas in the rotor chamber 11 from leaking toward the bearings 42, 44, and to prevent the lubricating oil supplied to the bearings 42, 44 from penetrating into the rotor chamber 11.

[0056] Therefore, in the oil-free screw compressor 1 of the present invention, as in the conventional oil-free screw compressor 100 described with reference to Figure 6, the aforementioned air seals 61, 62, oil seals 63, 64, cylindrical roller bearings 42a, 44a, spacer rings 42c, 44c, and angular bearings 42b, 44b are arranged between the inner walls of the first and second shaft holes 12, 13 provided in the cylinder 10 and the outer surfaces of the discharge side rotor shafts 22, 32, and the bearings 42, 44 are attached by first and second pressure plates 17, 18 attached to the discharge side end of the cylinder 10 where the ends of the shaft holes 12, 13 are open, fixing the outboard end faces of the outer rings of the first and second bearings 42, 44, specifically the outboard end faces of the outer rings of the angular bearings 42b, 44b, so as to press them toward the rotor chamber 11, thereby installing the bearings 42, 44.

[0057] Here, the rotor shafts 21, 22 provided on the first (male) screw rotor 20, to which rotational driving force is input from a driving source not shown, are formed relatively thick so as to obtain the necessary strength as the driving side, while the rotor shafts 31, 32 provided on the second (female) screw rotor 30 are formed thinner than the rotor shafts 21, 22 of the first screw rotor 20.

[0058] In addition, the second bearing 44 that supports the discharge side rotor shaft 32 of the second screw rotor 30, which has a small diameter, is smaller than the first bearing 42 that supports the discharge side rotor shaft 22 of the first screw rotor 20, which has a large diameter.

[0059] In this way, the discharge side rotor shaft 32 of the second screw rotor 30 is formed thinner than the discharge side rotor shaft 22 of the first screw rotor 20 and is supported by a small bearing 44, and the second timing gear 52 attached to the discharge side rotor shaft 32 of the second (female) screw rotor 30 has a larger diameter than the first timing gear attached to the discharge side rotor shaft 22 of the first (male) screw rotor 20, so that at least a portion of the head of the fixing bolt 19b that fixes the second pressure plate 18 is positioned inside the outer diameter circle of the second timing gear 52, as shown in Figure 2 (B).

[0060] In contrast, the first timing gear 51 attached to the discharge side rotor shaft 22 of the first (male) screw rotor 20 is thicker than the second discharge side rotor shaft 32 and is supported by a large first bearing 42, and is smaller in diameter than the second timing gear attached to the discharge side rotor shaft 32 of the second (female) screw rotor 30, so the head of the fixing bolt 19a that fixes the first pressure plate 17 is positioned outside the outer diameter circle of the first timing gear 51 as shown in Figure 2 (B).

[0061] Furthermore, as mentioned above, the second bearing 44 provided on the second (female) screw rotor 30 side is smaller than the first bearing 42 provided on the first (male) screw rotor 20 side, and therefore the axial length of the second bearing 44 is shorter than that of the first bearing 42.

[0062] Here, in the conventional oil-free screw compressor 100 described with reference to Figure 6(A), a cylindrical spacer 118a is provided on the pressure plate 118 used to fix the bearing 144 that supports the discharge side rotor shaft 132 provided on the female screw rotor 130, and the outer ring of the angular bearing 142b of the bearing 142 is fixed via this spacer 118a, so that the side of the pressure plate 117 provided on the male screw rotor 120 side facing the timing gear 151 and the side of the pressure plate 118 provided on the female screw rotor 130 side facing the timing gear 152 are arranged on the same plane.

[0063] In contrast, in the oil-free screw compressor 1 of the present invention, without providing such a cylindrical spacer 118a, a configuration is adopted in which the outboard end faces of the outer rings of the angular bearings 42b, 44b of the first and second bearings 42, 44 are directly fixed by the side faces of the first and second pressure plates 17, 18, thereby making the distance Lcf from the discharge side end face 30a of the second screw rotor 30 to the side face of the second pressure plate 18 on the timing gear 52 side shorter than the distance Lcm from the discharge side end face 20a of the first screw rotor 20 to the side face of the first pressure plate 17 on the timing gear 51 side.

[0064] As a result, even if the distance Wm between the first pressure plate 17 on the first (male) screw rotor 20 side and the first timing gear 51 is made narrower than the thickness Tm of the head of the fixing bolt 19a that fixes the first pressure plate 17, the distance Wf between the second pressure plate 18 on the second (female) screw rotor 30 side and the second timing gear 52 can be made wider than the thickness Tf of the head of the fixing bolt 19b that fixes the second pressure plate 18, thereby making it possible to avoid interference between the two, and the lengths of the discharge side rotor shafts 22, 32 of the first and second screw rotors 20, 30 can be made as short as possible.

[0065] In the embodiment shown in Figure 2, the distance Wm between the first pressure plate 17 and the first timing gear 51 is made narrower than the thickness Tm of the head of the fixing bolt 19a that fixes the first pressure plate 17.

[0066] However, the distance Lcf from the discharge side end face 30a of the second screw rotor 30 to the side face of the second pressing plate 18 on the timing gear 52 side is made shorter than the distance Lcm from the discharge side end face 20a of the first screw rotor 20 to the side face of the first pressing plate 17 on the timing gear 51 side, and the interval Wf between the second pressing plate 18 and the second timing gear 52 is made wider than the thickness Tf of the head of the fixing bolt 19b that fixes the second pressing plate 18. If this can be done, even if the distance Wm between the first pressure plate 17 and the first timing gear 51 is formed wider than the thickness Tm of the head of the fixing bolt 19a that fixes the first pressure plate 17, it is possible to avoid interference between the heads of the fixing bolts 19b that fix the second timing gear 52 and the second pressure plate 18, and to shorten the length of the discharge side rotor shafts 22, 32 of the first and second screw rotors 20, 30 compared to the conventional structure shown in Figure 6.

[0067] Therefore, the present invention is not limited to a configuration in which the distance Wm between the first pressure plate 17 and the first timing gear 51 is formed narrower than the thickness Tm of the head of the fixing bolt 19a that fixes the first pressure plate 17, as shown in Figure 2(A).

[0068] In this way, by making the length of the discharge side rotor shafts 22, 32 of the first and second screw rotors 20, 30 as short as possible, the moment load applied to the cylindrical roller bearings 42a, 44a could be reduced, thereby improving the lifespan of the cylindrical roller bearings 42a, 44a.

[0069] In addition, by shortening the overall length of the discharge side rotor shafts 22, 32, the overall length of the cylinder 10 can be shortened, making it possible to make the entire device smaller and lighter, and by shortening the overall length of the first and second shaft holes 12, 13, processability can also be improved.

[0070] In the embodiment shown in Figures 1 and 2(A), the opening ends 12a, 13a of both the first shaft hole 12 and the second shaft hole 13 are positioned on the same plane at the discharge side end 10a of the cylinder 10, and of the first and second bearings 42, 44, portions of the angular bearings 42b, 44b are installed so as to protrude outward from the opening ends 12a, 13a of the first and second shaft holes 12, 13.

[0071] In this way, by installing the angular bearings 42b, 44b of the first and second bearings 42, 44 so that a portion of them protrudes from the first and second axial holes 12, 13, the overall length of the first and second axial holes 12, 13 formed in the cylinder 10 can be further shortened, improving the workability of the first and second axial holes 12, 13 and enabling the cylinder 10 to be made smaller, thereby achieving a smaller and lighter oil-free screw compressor 1.

[0072] Furthermore, by shortening the overall length of the first and second shaft holes 12, 13, the ease of attachment / detachment and visual inspection of the oil seals 63, 64 and air seals 61, 62 that are attached in recessed positions in the first and second shaft holes 12, 13, respectively, can be improved.

[0073] On the other hand, in the illustrated embodiment, the angular bearings 42b, 44b are mounted with recesses 12b, 13b in the first and second shaft holes 12, 13 so that they only bear thrust loads and are not subjected to radial loads, and the outer rings of the angular bearings 42b, 44b are not fixed by the inner walls of the shaft holes 12, 13 even in the parts inserted into the first and second shaft holes 12, 13.

[0074] Therefore, even if a portion of the angular bearings 42b, 44b is exposed from the shaft holes 12, 13 as shown in FIG. 2(A), no functional problems will arise.

[0075] As explained with reference to Figure 2(A), in a configuration in which the opening end 12a of the first shaft hole 12 and the opening end 13a of the second shaft hole 13 are both arranged on the same plane at the discharge side end 10a of the cylinder 10 and the overall lengths of both shaft holes 12, 13 are the same, the first bearing 42, which has a longer axial length, has a longer protruding length of the bearing 42 (angular bearing 42b), and the gap δm formed between the opening end 12a of the first shaft hole 12 and the first pressure plate 17 is wider than the gap δf formed between the opening end 13a of the second shaft hole 13 and the second pressure plate 18.

[0076] As a result, if the fixing bolts 19a used to fix the first pressure plate 17 and the fixing bolts 19b used to fix the second pressure plate 18 are the same length, the threading depth of the fixing bolts 19a that fix the first pressure plate 17 to the cylinder 10 will be shallow, and the attachment strength of the first pressure plate 17 will be low.

[0077] Therefore, in the embodiment shown in Figure 2(A), the length of the fixing bolts 19a used to fix the first pressure plate 17 is made longer than the length of the fixing bolts 19b used to fix the second pressure plate 18, so that the fixing bolts 19a and 19b are both screwed into the cylinder 10 to the same depth.

[0078] However, if different standards are used for the fixing bolts 19a of the first pressure plate 17 and the fixing bolts 19b of the second pressure plate 18, the increased number of parts will reduce workability during assembly and will result in increased manufacturing costs.

[0079] Therefore, in the embodiment shown in Figure 3, a bulge portion 10b is provided around the opening end 12a of the first axial hole 12, including the mounting position of the fixing bolt 19a of the first pressure plate 17, by bulging the discharge side end 10a of the cylinder 10 toward the first timing gear 51, so that the gap δm between the first pressure plate 17 and the opening end 12a of the first axial hole 12 and the gap δf between the second pressure plate 18 and the opening end 13a of the second axial hole 13 are the same width.

[0080] In this way, by configuring the gap δm between the first pressure plate 17 and the opening end 12a of the first shaft hole 12 and the gap δf between the second pressure plate 18 and the opening end 13a of the second shaft hole 13 to be the same width, the fixing bolts 19a of the first pressure plate 17 and the fixing bolts 19b of the second pressure plate 18 can be made the same length, and as a result, compared to using fixing bolts of different sizes to fix the first pressure plate 17 and the second pressure plate 18, it is possible to reduce costs by sharing parts and simplify assembly work, etc.

[0081] In the embodiment shown in Figure 3, in order to make the gap δm between the first pressure plate 17 and the opening end 12a of the first shaft hole 12 and the gap δf between the second pressure plate 18 and the opening end 13a of the second shaft hole 13 the same width, a configuration is adopted in which a bulging portion 10b is provided in which the periphery of the opening 12a of the first shaft hole 12 bulges toward the first timing gear 51.However, instead of this configuration, a configuration may be adopted in which a recessed portion 10c is formed in which the periphery of the opening end 13a of the second shaft hole 13 is recessed toward the rotor chamber 11, as shown in Figure 4(A).

[0082] In the embodiment shown in Figure 4, in order to reduce the gap δm between the first pressure plate 17 and the opening end 12a of the first shaft hole 12, the opening end 12a of the first shaft hole 12 is extended to a position near the outboard end face of the outer ring of the first bearing 42, and a recessed portion 10c is formed by recessing the periphery of the opening end 13a of the second shaft hole 13 toward the rotor chamber 11.The opening end 13a of the second shaft hole 13 is provided within this recessed portion 10c, and the second pressure plate 18 is fitted into this recessed portion 10c so that the gap δf between the second pressure plate 18 and the opening end 13a of the second shaft hole 13 is the same as the gap δm between the first pressure plate 17 and the opening end 12a of the first shaft hole 12.

[0083] In this configuration, by setting the gaps δm and δf to the minimum necessary width, not only can the fixing bolts 19a, 19b of the first and second pressure plates 17, 18 be made the same length, but when fixing bolts 19a, 19b of the same length as in the embodiment described with reference to Figure 3 are used, the fixing bolts 19a, 19b can be screwed deeper into the cylinder 10, and even when fixing bolts 19a, 19b that are shorter than those in the embodiment of Figure 3 are used, the required screwing depth can be ensured. [Explanation of symbols]

[0084] 1 Oil-free screw compressor 10 cylinders 10a Discharge end (of cylinder) 10b Bulge 10c Depression 11 Rotor Room 12 First shaft hole (discharge side) 12a Open end (of first shaft hole) 12b Recess (first shaft hole) 13 Second shaft hole (discharge side) 13a Open end (of second shaft hole) 13b Recess (of the second shaft hole) 14 Inlet casing 15,16 Shaft hole (intake side) 17 First holding plate 18 Second pressure plate 19a Fixing bolt (for first holding plate) 19b Fixing bolt (for second holding plate) 20 No. 1 (male) screw rotor 20a Discharge side end surface (of the first (male) screw rotor) 21 Intake side rotor shaft 22 Discharge side rotor shaft 30 Second (female) screw rotor 30a Discharge side end surface (of the second (female) screw rotor) 31 Intake side rotor shaft 32 Discharge side rotor shaft 41 Bearing (suction side) 42 First bearing (discharge side) 42a Cylindrical roller bearing 42b angular contact bearing 42c spacer ring 43 Bearing (suction side) 44 Second bearing (discharge side) 44a cylindrical roller bearing 44b angular contact bearing 44c spacer ring 51 First timing gear 52 Second timing gear 61,62 Air seal 63,64 Oil seal 100 Oil-free screw compressor 110 cylinders 110a Discharge side end (of cylinder) 111 Rotor Room 112, 113 Shaft hole (discharge side) 112a, 113a Open end (of shaft hole) 114 Inlet casing 115,116 Shaft hole (intake side) 117,118 Presser plate 118a Cylindrical spacer 119a, 119b Fixing bolts 120 Male screw rotor 120a Discharge side end face (of male screw rotor) 121 Rotor shaft (suction side) 122 Rotor shaft (discharge side) 130 Female screw rotor 130a Discharge side end face (of female screw rotor) 131 Rotor shaft (suction side) 132 Rotor shaft (discharge side) 141,143 Bearing (suction side) 142,144 Bearing (discharge side) 142a, 144a Cylindrical roller bearings 142b, 144b Angular contact bearing 142c, 144c spacer ring 151,152 Timing gear 161,162 Air seal 163,164 Oil seal Lam: Distance between the discharge end face 120a of the male screw rotor 120 and the outboard end face of the angular bearing 142b (Fig. 6) Laf: Distance between the discharge side end surface 130a of the female screw rotor 130 and the outboard end surface of the angular bearing 144b (FIG. 6) Lb: The center distance in the thickness direction between the discharge side end faces 120a, 130a of the screw rotors 120, 130 and the timing gears 151, 152 (FIG. 6). Lc: Distance between the discharge end faces 120a, 130a of the screw rotors 120, 130 and the side faces of the pressure plates 117, 118 on the timing gear 151, 152 side (FIG. 6) L cm: distance between the discharge end surface 20a of the first (male) screw rotor 20 and the side surface of the first pressing plate 17 on the timing gear 51 side (FIGS. 2(A), 3(A), and 4(A)). Lcf: the distance between the discharge end surface 30a of the second (female) screw rotor 30 and the side surface of the second pressing plate 18 on the timing gear 52 side (FIGS. 2(A), 3(A), and 4(A)). Wm: Distance between timing gear 51, 151 and pressure plate 17, 117 Wf: Distance between timing gear 52, 152 and pressure plate 18, 118 Tm: Head thickness of fixing bolts 19a and 119a Tf: Head thickness of fixing bolts 19b and 119b δm: Gap (between the first pressing plate 17 and the opening end 12a of the first shaft hole 12) δf: Gap (between the second pressing plate 18 and the opening end 13a of the second shaft hole 13)

Claims

1. a cylinder having a rotor chamber for rotatably accommodating a first screw rotor, which is either a male or female screw rotor, and a second screw rotor, which is the other screw rotor, and having a first shaft hole into which the discharge side rotor shaft of the first screw rotor is inserted and a second shaft hole into which the discharge side rotor shaft of the second screw rotor is inserted; a first bearing attached to the first shaft hole and supporting the discharge side rotor shaft of the first screw rotor, and a second bearing attached to the second shaft hole and supporting the discharge side rotor shaft of the second screw rotor; a first pressing plate for fixing the first bearing and a second pressing plate for fixing the second bearing, which are respectively attached via fixing bolts to the discharge side end of the cylinder where the first and second axial holes open; a first timing gear attached to the discharge side rotor shaft of the first screw rotor passing through the first pressure plate, and a second timing gear attached to the discharge side rotor shaft of the second screw rotor passing through the second pressure plate, In an oil-free screw compressor, the axial length of the second bearing is formed shorter than that of the first bearing, and at least a portion of the fixing bolt that fixes the second presser plate is arranged inside the outer diameter circle of the second timing gear, the first and second bearings are housed in the first and second axial holes so that portions of the first and second bearings protrude beyond the open ends of the first and second axial holes, and the ends of the first and second bearings protruding from the first and second axial holes are fixed by cylinder-side side surfaces of the first and second pressure plates attached to the discharge-side end of the cylinder with a gap formed between the first and second bearings and the open ends of the first and second axial holes, and the distance from the discharge-side end face of the second screw rotor to the side surface of the second pressure plate on the second timing gear side is made shorter than the distance from the discharge-side end face of the first screw rotor to the side surface of the first pressure plate on the first timing gear side, thereby forming a gap between the second pressure plate and the second timing gear wider than the thickness of the heads of the fixing bolts that fix the second pressure plate.

2. the fixing bolts for fixing the first pressing plate are disposed outside the outer diameter circle of the first timing gear, 2. An oil-free screw compressor according to claim 1, wherein the gap between the first pressure plate and the first timing gear is formed narrower than the thickness of the head of the fixing bolt that fixes the first pressure plate.

3. The first and second bearings each include a cylindrical roller bearing arranged on the rotor chamber side and an angular bearing arranged on the machine outboard side relative to the cylindrical roller bearing, 3. An oil-free screw compressor according to claim 1, wherein the first and second bearings are housed within the first and second axial holes so that a portion of the angular bearings provided on each of the first and second bearings protrudes from the open ends of the first and second axial holes.

4. An oil-free screw compressor according to claim 3, characterized in that the gap between the first pressure plate and the opening end of the first axial hole and the gap between the second pressure plate and the opening end of the second axial hole have the same width.

5. 5. An oil-free screw compressor according to claim 4, wherein the fixing bolts used to fix the first pressure plate and the fixing bolts used to fix the second pressure plate are bolts of the same size.

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