Screw compressor
By setting the suction completion timing of both rotor-side working chambers later than the reference but before pressure wave propagation, the screw compressor increases suction volume effectively despite small wrap angles, addressing efficiency issues.
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- HITACHI IND EQUIP SYST CO LTD
- Filing Date
- 2024-06-21
- Publication Date
- 2026-06-03
AI Technical Summary
Existing screw compressors face challenges in increasing suction amount when the wrap angle of the female rotor is small, as setting the suction completion timing later than the reference timing is hindered by pressure wave propagation and results in decreased suction.
The suction completion timing of both male- and female-rotor-side working chambers is set later than the reference timing but earlier than the propagation time of pressure waves, ensuring the wrap angles remain small.
This configuration enhances suction amount by leveraging gas inertia while preventing pressure wave discharge via the suction port, thus maintaining efficiency despite small wrap angles.
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Abstract
Description
Technical Field
[0001] The present invention relates to a screw compressor.Background Art
[0002] A screw compressor described in Patent Document 1 includes a male rotor which includes a lobe section in which a plurality of grooves are formed, a female rotor which includes a lobe section in which a plurality of grooves are formed, and is disposed so as to mesh with the male rotor, a plurality of male-rotor-side working chambers each formed in each of the plurality of grooves of the male rotor, and a plurality of female-rotor-side working chambers each formed in each of the plurality of grooves of the female rotor.
[0003] The male-rotor-side working chambers and the female-rotor-side working chambers move as the male rotor and the female rotor rotate, and volumes thereof change. The male-rotor-side working chambers and the female-rotor-side working chambers are configured to sequentially execute a suction phase in which gas is suctioned from a suction flow passage via a suction port (opening), a compression phase in which volumes of the working chambers are reduced to compress the gas, and a discharge phase in which the compressed gas is discharged to a discharge flow passage via a discharge port (opening).Prior Art DocumentPatent Document
[0004] Patent Document 1 JP-H06-288369-ASummary of the InventionProblem to be Solved by the Invention
[0005] A suction completion timing of the female-rotor-side working chamber in Patent Document 1 is the same as or earlier than a reference timing at which the volume of the female-rotor-side working chamber is the maximum, but when the suction completion timing is later than the reference timing, it is possible to increase a suction amount through an action of inertia of the suctioned gas. However it is not possible to set the suction completion timing of the female-rotor-side working chamber later than the reference timing unless a condition given by Expression (1) is satisfied. δf > Zf − Zm × 360 / Zf
[0006] δf [degree] of Expression (1) denotes a rotation angle range of the female rotor in which a female-rotor-side working chamber having the maximum volume out of the plurality of female-rotor-side working chambers exists (hereinafter referred to as female-rotor-side maximum volume existence angle). Border lines between a wall surface of a male-rotor-side bore and a wall surface of a female-rotor-side bore are referred to as low-pressure-side cusp and high-pressure-side cusp, and a rotation angle range φCf [degree] of the female rotor corresponding to a circumferential width between the low-pressure-side cusp and the high-pressure-side cusp is defined. In this rotation angle range φCf of the female rotor, the lobe of the male rotor exists, and hence the volume of the female-rotor-side working chamber does not become the maximum. Thus, the female-rotor-side maximum volume existence angle δf is obtained by subtracting a wrap angle φAf [degree] of the female rotor from a rotation angle range φBf [degree] (note that φBf = 360 - φCf) of the female rotor corresponding to a circumferential width of the wall surface of the female-rotor-side bore. The female-rotor-side maximum volume existence angle δf increases as the wrap angle φAf of the female rotor decreases.
[0007] The condition given by Expression (1) is such a condition that the female-rotor-side maximum volume existence angle δf is larger than a product of a number (Zf-Zm) obtained by subtracting a number of lobes Zm of the male rotor from a number of lobes Zf of the female rotor and a rotation angle range (360 / Zf) of the female rotor corresponding to a circumferential width of the groove of the female rotor. If the wrap angle φAf of the female rotor is so large that the condition given by Expression (1) is not satisfied, the male-rotor-side working chamber communicating with the female-rotor-side working chamber is in the compression phase when the volume of the female-rotor-side working chamber is the maximum. Thus, the compressed air in the male-rotor-side working chamber is possibly discharged via the female-rotor-side working chamber. Thus, the suction completion timing of the female-rotor-side working chamber cannot be set to be later than the reference timing.
[0008] Meanwhile, when the wrap angle φAf of the female rotor is so small that the condition given by Expression (1) is satisfied, it is possible to set the suction completion timing of the female-rotor-side working chamber later than the reference timing, thereby being able to increasing a suction amount. However, when the female-rotor-side working chamber reaches a discharge-side end surface of the lobe section of the female rotor, there is generated a pressure wave (counterflow) which is reflected on the inner wall of a casing opposing the discharge-side end surface of the lobe section of the female rotor, and propagates toward a suction-side end surface of the lobe section of the female rotor. Thus, when the suction completion timing of the female-rotor-side working chamber is too late, the pressure wave described above is discharged via the suction port, and hence the suction amount decreases.
[0009] The present invention has been made in view of the matter described above, and has an object to increase a suction amount under such a condition that a wrap angle of a female rotor is small.Means for Solving the Problem
[0010] In order to solve the problem described above, a configuration described in CLAIMS is applied. The present invention includes a plurality of means for solving the problem described above, and one example thereof is a screw compressor including a male rotor that includes a lobe section in which a plurality of grooves are formed, a female rotor that includes a lobe section in which a plurality of grooves are formed, and is disposed so as to mesh with the male rotor, a plurality of male-rotor-side working chambers each formed in each of the plurality of grooves of the male rotor, and a plurality of female-rotor-side working chambers each formed in each of the plurality of grooves of the female rotor, a rotation angle range of the female rotor in which a female-rotor-side working chamber having a maximum volume, out of the plurality of female-rotor-side working chambers, exists is larger than a product of a number obtained by subtracting a number of lobes of the male rotor from a number of lobes of the female rotor and a rotation angle range of the female rotor corresponding to a circumferential width of the groove of the female rotor, and a suction completion timing of the female-rotor-side working chamber is set to be later than a reference timing at which a volume of the female-rotor-side working chamber is the maximum, and is set to be earlier than elapse of a propagation time of a pressure wave that propagates from a discharge-side end surface to a suction-side end surface of the lobe section of the female rotor in the female-rotor-side working chamber.Advantages of the Invention
[0011] According to the present invention, it is possible to increase the suction amount under the condition that the wrap angle of the rotor is small.
[0012] Note that problems, configurations, and effects other than those described above will be made clear by the following description.Brief Description of the Drawings
[0013] [Fig. 1] Fig. 1 is a cross-sectional view for illustrating a structure of a screw compressor according to one embodiment of the present invention. [Fig. 2] Fig. 2 is a cross-sectional view made on a plane and in a direction indicated by arrows II of Fig. 1. [Fig. 3] Fig. 3 is a cross-sectional view made on a plane and in a direction indicated by arrows III of Fig. 2. [Fig. 4] Fig. 4 is a cross-sectional view made on a plane and in a direction indicated by arrows IV of Fig. 2. [Fig. 5] Fig. 5 is a development view of a lobe section of a female rotor for illustrating a plurality of female-rotor-side working chambers in the embodiment of the present invention together with a part of a suction port. [Fig. 6] Fig. 6 is a development view of a lobe section of a male rotor for illustrated a plurality of male-rotor-side working chambers in the embodiment of the present invention together with a part of the suction port. Modes for Carrying Out the Invention
[0014] A description is now given of an embodiment of the present invention with reference to the drawings.
[0015] Fig. 1 is a cross-sectional view for illustrating a structure of a screw compressor according to the present embodiment (cross-sectional view made on a plane and in a direction indicated by arrows I of Fig. 2), and Fig. 2 is a cross-sectional view made on a plane and in a direction indicated by arrows II of Fig. 1. Fig. 3 is a cross-sectional view made on a plane and in a direction indicated by arrows III of Fig. 2, and Fig. 4 is a cross-sectional view made on a plane and in a direction indicated by arrows IV of Fig. 2. Note that, in Fig. 4, a discharge port, a discharge flow passage, and the like are not illustrated for the sake of convenience.
[0016] The screw compressor according to the present embodiment includes a male rotor 1A, a female rotor 1B which is disposed so as to mesh with the male rotor 1A, and a casing 2 which stores the male rotor 1A and the female rotor 1B.
[0017] The male rotor 1A includes a lobe section 3A which includes a plurality (six in the present embodiment) of helical lobes and a plurality of grooves each formed between the lobes, a suction-side shaft section 4A connected to one side (left side of Fig. 1 and Fig. 2) of the lobe section 3A in an axial direction, and a discharge-side shaft section 5A connected to another side (right side of Fig. 1 and Fig. 2) of the lobe section 3A in the axial direction. The suction-side shaft section 4A of the male rotor 1A is rotatably supported by a suction-side bearing 6A, and the discharge-side shaft section 5A of the male rotor 1A is rotatably supported by a discharge-side bearing 7A.
[0018] The female rotor 1B includes a lobe section 3B which includes a plurality (eight in the present embodiment) of helical lobes and a plurality of grooves each formed between the lobes, a suction-side shaft section 4B connected to one side (left side of Fig. 2) of the lobe section 3B in an axial direction, and a discharge-side shaft section 5B connected to another side (right side of Fig. 2) of the lobe section 3B in the axial direction. The suction-side shaft section 4B of the female rotor 1B is rotatably supported by a suction-side bearing 6B, and the discharge-side shaft section 5B of the female rotor 1B is rotatably supported by a discharge-side bearing 7B.
[0019] The suction-side shaft section 4A of the male rotor 1A passes through the casing 2, and is coupled to a rotation shaft (not depicted) of a motor. As a result, a rotational force of the motor is transmitted to the male rotor 1A, and hence the male rotor 1A rotates. The lobe section 3B of the female rotor 1B is in contact with and meshes with the lobe section 3A of the male rotor 1A. As another example, while the lobe section 3B of the female rotor 1B is disposed such that the lobe section 3B is not in contact with but meshes with the lobe section 3A of the male rotor 1A, a pair of timing gears (not depicted) are provided to the discharge-side shaft section 5A of the male rotor 1A and the discharge-side shaft section 5B of the female rotor 1B, and the pair of timing gears mesh with each other. As a result, the rotational force of the male rotor 1A is transmitted to the female rotor 1B, and hence the female rotor 1B rotates.
[0020] The casing 2 is formed of, for example, a main casing 8 and a suction-side casing 9 connected to the main casing 8. The main casing 8 includes a male-rotor-side bore 11A which accommodates the lobe section 3A of the male rotor 1A and forms a plurality of male-rotor-side working chambers 10A in the plurality of grooves thereof, and a female-rotor-side bore 11B which accommodates the lobe section 3B of the female rotor 1B and forms a plurality of female-rotor-side working chambers 10B in the plurality of grooves thereof. The male-rotor-side bore 11A and the female-rotor-side bore 11B partially overlap each other, and include a low-pressure-side cusp 12 and a high-pressure-side cusp 13 as border lines between wall surfaces thereof.
[0021] The male-rotor-side working chambers 10A and the female-rotor-side working chambers 10B move as the male rotor 1A and the female rotor 1B rotate, and volumes thereof change. The male-rotor-side working chambers 10A and the female-rotor-side working chambers 10B are configured to sequentially execute a suction phase in which gas (for example, air) is suctioned from a suction flow passage 15 via a suction port 14 (opening), a compression phase in which volumes of the working chambers are reduced to compress the gas, and a discharge phase in which the compressed gas (for example, compressed air) is discharged to a discharge flow passage 17 via a discharge port 16 (opening).
[0022] In the present embodiment, for reasons such as a reduction of a leak time through reduction of a compression time, a wrap angle φAf of the male rotor 1A and a wrap angle φAm of the female rotor 1B are configured to be small, and the condition given by Expression (1) is satisfied. For example, the wrap angle φAm of the female rotor 1B is 150, a rotation angle range φBf of the female rotor 1B corresponding to a circumferential width of the wall surface of the female-rotor-side bore 11B is 285, and hence a female-rotor-side maximum volume existence angle δf is 135. A product of a number (Zf - Zm) obtained by subtracting a number of lobes Zm of the male rotor 1A from a number of lobes Zf of the female rotor 1B and a rotation angle range (360 / Zf) of the female rotor 1B corresponding to a circumferential width of the groove of the female rotor 1B is 90, and hence satisfies the condition given by Expression (1). Thus, a suction completion timing of the male-rotor-side working chamber 10A can be later than a reference timing, and a suction completion timing of the female-rotor-side working chamber 10B can also be later than a reference timing.
[0023] First, with reference to Fig. 5, a description is now given of the suction completion timing of the female-rotor-side working chamber 10B (in other words, a timing at which the suction port 14 is closed by a closing section 20 of the suction-side casing 9 for the female-rotor-side working chamber 10B) in the present embodiment.
[0024] Fig. 5 is a development view of the lobe section 3B of the female rotor 1B for illustrating the plurality of female-rotor-side working chambers 10B in the embodiment together with a part of the suction port 14. Note that a vertical direction of Fig. 5 is the axial direction of the lobe section 3B of the female rotor 1B. A horizontal direction of Fig. 5 is the circumferential direction of the lobe section 3B of the female rotor 1B, and a position thereof is indicated as the rotation angle of the female rotor 1B (in details, a rotation angle with respect to 0 that indicates a position of a straight line connecting a rotation center of the male rotor 1A and a rotation center of the female rotor 1B to each other). In Fig. 5, a plurality of diagonal lines indicate a plurality of lobe tips which partition the plurality of female-rotor-side working chambers 10B, and a hatched one of the plurality of female-rotor-side working chambers 10B indicates a suction completion state.
[0025] In the present embodiment, the suction completion timing of the female-rotor-side working chamber 10B is set to be later than the reference timing at which the volume of the female-rotor-side working chamber 10B is the maximum (in other words, a reference timing at which the volume of the female-rotor-side working chamber 10B changes from a state in which the volume is not the maximum to the state in which the volume is the maximum), and is set to be earlier than elapse of a propagation time of a pressure wave which propagates from a discharge-side end surface 18B to a suction-side end surface 19B of the lobe section 3B of the female rotor 1B in the female-rotor-side working chamber 10B. A description is now given of details thereof.
[0026] It is assumed that, when a leading lobe tip, out of the leading lobe tip and a trailing lobe tip which partition the female-rotor-side working chamber 10B, reaches the low-pressure-side cusp 12 on the discharge-side end surface 18B of the lobe section 3B of the female rotor 1B, there is generated a pressure wave (counterflow) which is reflected on the inner wall of the main casing 8 opposing the discharge-side end surface 18B of the lobe section 3B of the female rotor 1B, and propagates toward the suction-side end surface 19B of the lobe section 3B of the female rotor 1B. A propagation time of the pressure wave which propagates from the discharge-side end surface 18B to the suction-side end surface 19B of the lobe section 3B of the female rotor 1B is obtained by dividing a groove length Lf of the female rotor 1B by a sound speed "a." Thus, when a position of the low-pressure-side cusp 12 is set to a reference, a rotation angle φLMTf of the female rotor 1B (hereinafter referred to as female-rotor-side counterflow limit angle φLMTf) which extends until the pressure wave reaches, from the discharge-side end surface 18B of the lobe section 3 of the female rotor 1B, the suction-side end surface 19B is given by Expression (2). ωf in the expression is an angular velocity of the female rotor 1B. φLMTf = Lf / a × ωf
[0027] As illustrated in Fig. 5, there is assumed a rotation angle φDf of the female rotor (hereinafter referred to as female-rotor-side suction completion angle φDf) which is set at a position of the leading lobe tip on the discharge-side end surface 18B of the lobe section 3B of the female rotor 1B with respect to the position of the low-pressure-side cusp 12 as the reference, and at which the suction of the female-rotor-side working chamber 10B is completed. The female-rotor-side suction completion angle φDf is set so as to be smaller than the female-rotor-side counterflow limit angle φLMTf. As a result, the suction completion timing of the female-rotor-side working chamber 10B is set to be earlier than elapse of a propagation time (Lf / a) of the pressure wave which propagates from the discharge-side end surface 18B to the suction-side end surface 19B of the lobe section 3B of the female rotor 1B in the female-rotor-side working chamber 10B.
[0028] With reference to Fig. 6, a description is now given of the suction completion timing of the male-rotor-side working chamber 10A (in other words, a timing at which the suction port 14 is closed by the closing section 20 of the suction-side casing 9 for the male-rotor-side working chamber 10A) in the present embodiment.
[0029] Fig. 6 is a development view of the lobe section 3A of the male rotor 1A for illustrating the plurality of male-rotor-side working chambers 10A in the embodiment together with a part of the suction port 14. Note that a vertical direction of Fig. 6 is the axial direction of the lobe section 3A of the male rotor 1A. A horizontal direction of Fig. 6 is the circumferential direction of the lobe section 3A of the male rotor 1A, and a position thereof is indicated as the rotation angle of the male rotor 1A (in details, a rotation angle with respect to 0 that indicates a position of the straight line connecting the rotation center of the male rotor 1A and the rotation center of the female rotor 1B to each other). In Fig. 6, a plurality of diagonal lines indicate a plurality of lobe tips which partition the plurality of male-rotor-side working chambers 10A, and a hatched one of the plurality of male-rotor-side working chambers 10A indicates the suction completion state.
[0030] In the present embodiment, the suction completion timing of the male-rotor-side working chamber 10A is set to be later than the reference timing at which the volume of the male-rotor-side working chamber 10A is the maximum (in other words, a reference timing at which the volume of the male-rotor-side working chamber 10A changes from the state in which the volume is not the maximum to the state in which the volume is the maximum), and is set to be earlier than elapse of a propagation time of the pressure wave which propagates from a discharge-side end surface 18A to a suction-side end surface 19A of the lobe section 3A of the male rotor 1A in the male-rotor-side working chamber 10A. A description is now given of details thereof.
[0031] It is assumed that, when a leading lobe tip, out of the leading lobe tip and a trailing lobe tip which partition the male-rotor-side working chamber 10A, reaches the low-pressure-side cusp 12 on the discharge-side end surface 18A of the lobe section 3A of the male rotor 1A, there is generated a pressure wave (counterflow) which is reflected on the inner wall of the main casing 8 opposing the discharge-side end surface 18A of the lobe section 3A of the male rotor 1A and propagates toward the suction-side end surface 19A of the lobe section 3A of the male rotor 1A. A propagation time of the pressure wave which propagates from the discharge-side end surface 18A to the suction-side end surface 19A of the lobe section 3A of the male rotor 1A is obtained by dividing a groove length Lm of the male rotor 1A by the sound speed "a." Thus, when the position of the low-pressure-side cusp 12 is set to a reference, a rotation angle φLMTm of the male rotor 1A (hereinafter referred to as male-rotor-side counterflow limit angle φLMTm) which extends until the pressure wave reaches the suction-side end surface 19A of the lobe section 3A of the male rotor 1A is given by Expression (3). ωm in the expression is an angular velocity of the male rotor 1A. φLMTm = Lm / a × ωm
[0032] As illustrated in Fig. 6, there is assumed a rotation angle φDm of the male rotor 1A (hereinafter referred to as male-rotor-side suction completion angle φDm) which is set at a position of the leading lobe tip on the discharge-side end surface 18A of the lobe section 3A of the male rotor 1A with respect to the position of the low-pressure-side cusp 12 as the reference, and at which the suction of the male-rotor-side working chamber 10A is completed. The male-rotor-side suction completion angle φDm is set so as to be smaller than the male-rotor-side counterflow limit angle φLMTm. As a result, the suction completion timing of the male-rotor-side working chamber 10A is set to be earlier than elapse of a propagation time (Lm / a) of the pressure wave which propagates from the discharge-side end surface 18A to the suction-side end surface 19B of the lobe section 3A of the male rotor 1A in the male-rotor-side working chamber 10A.
[0033] As described above, in the present embodiment, the suction completion timing of the female-rotor-side working chamber 10B is set to be later than the reference timing and earlier than the elapse of the propagation time (Lf / a) of the pressure wave. Moreover, the suction completion timing of the male-rotor-side working chamber 10A is set to be later than the reference timing and earlier than the elapse of the propagation time (Lm / a) of the pressure wave. As a result, a suction amount can be increased through an action of inertia of the suctioned gas as compared with a case in which the suction completion timing of the female-rotor-side working chamber 10B and the suction completion timing of the male-rotor-side working chamber 10A are not later than the reference timings. Moreover, unlike a case in which the suction completion timing of the female-rotor-side working chamber 10B and the suction completion timing of the male-rotor-side working chamber 10A are set to be later than the propagation times of the pressure waves, the pressure waves are not discharged via the suction port 14, and hence a decrease in the suction amount can be avoided. Thus, it is possible to increase the suction amount under such a condition that the wrap angles of the rotors are small.
[0034] Note that, in the embodiment described above, there is given the description that not only the suction completion timing of the female-rotor-side working chamber 10B, but also the suction completion timing of the male-rotor-side working chamber 10A is set to be later than the reference timing and earlier than the elapse of the propagation time of the pressure wave, but the configuration is not limited to this example. The suction completion timing of the male-rotor-side working chamber 10A may be set to be later than the elapse of the propagation time of the pressure wave or may be set to be the same as or earlier than the reference timing although the overall suction amount decreases as compared with the embodiment described above.Description of Reference Characters
[0035] 1A:male rotor 1B:female rotor 3A, 3B:lobe section 10A:male-rotor-side working chamber 10B:female-rotor-side working chamber 11A:male-rotor-side bore 11B:female-rotor-side bore 18A, 18B:discharge-side end surface 19A, 19B:suction-side end surface
Claims
1. A screw compressor, comprising: a male rotor that includes a lobe section in which a plurality of grooves are formed; a female rotor that includes a lobe section in which a plurality of grooves are formed, and is disposed so as to mesh with the male rotor; a plurality of male-rotor-side working chambers each formed in each of the plurality of grooves of the male rotor; and a plurality of female-rotor-side working chambers each formed in each of the plurality of grooves of the female rotor, wherein a rotation angle range of the female rotor in which a female-rotor-side working chamber having a maximum volume, out of the plurality of female-rotor-side working chambers, exists is larger than a product of a number obtained by subtracting a number of lobes of the male rotor from a number of lobes of the female rotor and a rotation angle range of the female rotor corresponding to a circumferential width of the groove of the female rotor, and a suction completion timing of the female-rotor-side working chamber is set to be later than a reference timing at which a volume of the female-rotor-side working chamber is maximum, and is set to be earlier than elapse of a propagation time of a pressure wave that propagates from a discharge-side end surface to a suction-side end surface of the lobe section of the female rotor in the female-rotor-side working chamber.
2. The screw compressor according to claim 1, wherein a suction completion timing of the male-rotor-side working chamber is set to be later than a reference timing at which a volume of the male-rotor-side working chamber is maximum, and is set to be earlier than elapse of a propagation time of a pressure wave that propagates from a discharge-side end surface to a suction-side end surface of the lobe section of the male rotor in the male-rotor-side working chamber.