Screw compressor

Abstract

Provided is a screw compressor making it possible to increase intake under conditions where a rotor has a small total winding angle. The screw compressor is provided with: a plurality of male rotor-side working chambers 10A formed in a plurality of tooth spaces of a male rotor 1A; and a plurality of female rotor-side working chambers 10B formed in a plurality of tooth spaces of a female rotor 1B. The female rotor 1B includes, from among the plurality of female rotor-side working chambers 10B, a working chamber having a maximum volume. A rotational angle range of the female rotor is greater than the product of: a number obtained by subtracting the number of teeth of the male rotor 1A from the number of teeth of the female rotor 1B; and a rotational angle range of the female rotor 1B corresponding to a circumferential direction width of the tooth spaces of the female rotor 1B. An intake completion timing of the female rotor-side working chambers 10B has been configured to be later than a reference timing at which the volume of the female rotor-side working chambers 10B reaches a maximum, and before a propagation time of pressure waves elapses, said waves propagating inside the female rotor-side working chambers 10B from a discharge-side end surface 18B to an intake-side end surface 19B of teeth 3B of the female rotor 1B.

Description

Screw Compressor

[0001] The present invention relates to a screw compressor.

[0002] The screw compressor of Patent Document 1 includes a male rotor having a tooth portion with a plurality of tooth grooves formed therein, a female rotor having a tooth portion with a plurality of tooth grooves formed therein and arranged to mesh with the male rotor, a plurality of male rotor side working chambers formed in the plurality of tooth grooves of the male rotor, and a plurality of female rotor side working chambers formed in the plurality of tooth grooves of the female rotor.

[0003] The male rotor side working chamber and the female rotor side working chamber move and change in volume as the male rotor and the female rotor rotate. The male rotor side working chamber and the female rotor side working chamber sequentially perform an intake stroke in which gas is drawn in from the intake passage through an intake port (opening), a compression stroke in which the volume is reduced to compress the gas, and a discharge stroke in which the compressed gas is discharged into the discharge passage through a discharge port (opening).

[0004] Japanese Patent Application Publication No. 06-288369

[0005] In Patent Document 1, the timing at which the intake of the female rotor working chamber is completed is the same as or earlier than the reference timing at which the volume of the female rotor working chamber is maximized, but if it is delayed, the intake volume can be increased by the inertial action of the intake gas. However, unless the condition of the following equation (1) is satisfied, the intake completion timing of the female rotor working chamber cannot be delayed from the reference timing: δf>(Zf-Zm)×(360 / Zf) (1)

[0006] In Equation (1), δf [degrees] represents the rotational angle range of the female rotor (hereinafter referred to as the female rotor maximum volume existence angle) within which the female rotor working chamber with the largest volume exists. The boundary lines between the wall surfaces of the male rotor bore and the female rotor bore are referred to as the low-pressure side cusp and the high-pressure side cusp, and the rotational angle range φCf [degrees] of the female rotor is defined as the circumferential width between the low-pressure side cusp and the high-pressure side cusp. Within this rotational angle range φCf, the volume of the female rotor working chamber does not reach its maximum due to the presence of male rotor teeth. Therefore, the female rotor maximum volume existence angle δf is calculated by subtracting the female rotor full wrap angle φAf [degrees] from the female rotor rotational angle range φBf [degrees] (where φBf = 360 - φCf) corresponding to the circumferential width of the wall surface of the female rotor bore. The female rotor maximum volume existence angle δf increases as the female rotor full wrap angle φAf decreases.

[0007] The condition of formula (1) is that the female rotor's maximum volume existence angle δf is greater than the product of the number of female rotor teeth Zf minus the number of male rotor teeth Zm (Zf - Zm) and the rotational angle range of the female rotor (360 / Zf) corresponding to the circumferential width of the female rotor tooth grooves. If the female rotor's total wrap angle φAf is large and does not satisfy the condition of formula (1), when the volume of the female rotor working chamber is at its maximum, the male rotor working chamber communicating with the female rotor working chamber will be in the compression stroke. As a result, there is a possibility that compressed air from the male rotor working chamber will be discharged via the female rotor working chamber. Therefore, the intake completion timing of the female rotor working chamber cannot be delayed from the reference timing.

[0008] On the other hand, if the female rotor's total wrap angle φAf is small and satisfies the condition of equation (1), the suction volume can be increased by delaying the suction completion timing of the female rotor working chamber from the reference timing. However, when the female rotor working chamber reaches the discharge end face of the female rotor teeth, a pressure wave (backflow) is generated that is reflected by the inner wall of the casing opposite the discharge end face of the female rotor teeth and moves toward the suction end face of the female rotor teeth. Therefore, if the suction completion timing of the female rotor working chamber is too late, the pressure wave is discharged through the suction port, reducing the suction volume.

[0009] The present invention has been made in view of the above circumstances, and one of its objects is to increase the intake amount under the condition that the total wrap angle of the female rotor is small.

[0010] The present invention includes a plurality of means for solving the above-mentioned problems, and one example thereof is a screw compressor including a male rotor having a toothed portion with a plurality of tooth grooves formed therein, a female rotor having a toothed portion with a plurality of tooth grooves formed therein and arranged to mesh with the male rotor, a plurality of male-rotor working chambers formed in the tooth grooves of the male rotor, and a plurality of female-rotor working chambers formed in the tooth grooves of the female rotor, wherein a rotational angle range of the female rotor in which one of the plurality of female-rotor working chambers having the largest volume is present is greater than the product of the number of teeth of the female rotor minus the number of teeth of the male rotor and the rotational angle range of the female rotor corresponding to the circumferential width of the tooth grooves of the female rotor, and the suction completion timing of the female-rotor working chamber is set later than a reference timing at which the volume of the female-rotor working chamber reaches its maximum and before the elapse of a propagation time for a pressure wave propagating within the female-rotor working chamber from a discharge-side end face of the toothed portion of the female rotor to a suction-side end face of the female rotor.

[0011] According to the present invention, the intake amount can be increased under the condition that the rotor wrap angle is small.

[0012] Problems, configurations, and effects other than those described above will become clear from the following description.

[0013] Fig. 1 is a cross-sectional view showing the structure of a screw compressor according to an embodiment of the present invention. Fig. 2 is a cross-sectional view taken along arrows II-II in Fig. 1. Fig. 3 is a cross-sectional view taken along arrows III-III in Fig. 2. Fig. 4 is a cross-sectional view taken along arrows IV-IV in Fig. 2. Fig. 5 is a development view of the teeth of a female rotor showing a plurality of female rotor-side working chambers together with a part of an intake port according to an embodiment of the present invention. Fig. 6 is a development view of the teeth of a male rotor showing a plurality of male rotor-side working chambers together with a part of an intake port according to an embodiment of the present invention.

[0014] An embodiment of the present invention will be described with reference to the drawings.

[0015] Fig. 1 is a cross-sectional view (cross-sectional view taken along arrows I-I in Fig. 2) showing the structure of a screw compressor in this embodiment, and Fig. 2 is a cross-sectional view taken along arrows II-II in Fig. 1. Fig. 3 is a cross-sectional view taken along arrows III-III in Fig. 2, and Fig. 4 is a cross-sectional view taken along arrows IV-IV in Fig. 2. Note that, for convenience, a discharge port, a discharge flow path, and the like are omitted from Fig. 4.

[0016] The screw compressor of this embodiment includes a male rotor 1A, a female rotor 1B arranged to mesh with the male rotor 1A, and a casing 2 that houses the male rotor 1A and the female rotor 1B.

[0017] The male rotor 1A comprises a toothed portion 3A having a plurality of (six in this embodiment) spiral teeth with a plurality of tooth grooves formed between the teeth, a suction-side shaft portion 4A connected to one axial side (left side in Figures 1 and 2) of the toothed portion 3A, and a discharge-side shaft portion 5A connected to the other axial side (right side in Figures 1 and 2) of the toothed portion 3A. The suction-side shaft portion 4A of the male rotor 1A is rotatably supported by a suction-side bearing 6A, and the discharge-side shaft portion 5A of the male rotor 1A is rotatably supported by a discharge-side bearing 7A.

[0018] The female rotor 1B has a toothed portion 3B having a plurality of (eight in this embodiment) spiral teeth with a plurality of tooth grooves formed between the teeth, a suction-side shaft portion 4B connected to one axial side (left side in FIG. 2) of the toothed portion 3B, and a discharge-side shaft portion 5B connected to the other axial side (right side in FIG. 2) of the toothed portion 3B. The suction-side shaft portion 4B of the female rotor 1B is rotatably supported by a suction-side bearing 6B, and the discharge-side shaft portion 5B of the female rotor 1B is rotatably supported by a discharge-side bearing 7B.

[0019] The suction-side shaft 4A of the male rotor 1A passes through the casing 2 and is connected to the rotating shaft of a motor (not shown). This transmits the rotational force of the motor to the male rotor 1A, causing it to rotate. The teeth 3B of the female rotor 1B contact and mesh with the teeth 3A of the male rotor 1A. Alternatively, the teeth 3B of the female rotor 1B are arranged to mesh with the teeth 3A of the male rotor 1A without contacting each other, but a pair of timing gears (not shown) are provided on the discharge-side shaft 5A of the male rotor 1A and the discharge-side shaft 5B of the female rotor 1B, and the pair of timing gears mesh with each other. This transmits the rotational force of the male rotor 1A to the female rotor 1B, causing it to rotate.

[0020] The casing 2 is composed of, for example, a main casing 8 and a suction-side casing 9 connected to the main casing 8. The main casing 8 has a male rotor-side bore 11A that houses the teeth 3A of the male rotor 1A and forms a plurality of male rotor-side working chambers 10A in the plurality of tooth spaces, and a female rotor-side bore 11B that houses the teeth 3B of the female rotor 1B and forms a plurality of female rotor-side working chambers 10B in the plurality of tooth spaces. The male rotor-side bore 11A and the female rotor-side bore 11B partially overlap each other and have a low-pressure-side cusp 12 and a high-pressure-side cusp 13 as the boundary between their wall surfaces.

[0021] The male rotor side working chamber 10A and the female rotor side working chamber 10B move and change in volume as the male rotor 1A and the female rotor 1B rotate. The male rotor side working chamber 10A and the female rotor side working chamber 10B sequentially perform an intake stroke in which gas (e.g., air) is drawn in from an intake passage 15 via an intake port 14 (opening), a compression stroke in which the volume is reduced to compress the gas, and a discharge stroke in which compressed gas (e.g., compressed air) is discharged to a discharge passage 17 via a discharge port 16 (opening).

[0022] In this embodiment, the total winding angle φAf of the male rotor 1A and the total winding angle φAm of the female rotor 1B are reduced by shortening the compression time and thereby shortening the leakage time, thereby satisfying the condition of the above formula (1). For example, the total winding angle φAm of the female rotor 1B is 150, and the rotational angle range φBf of the female rotor 1B corresponding to the circumferential width of the wall surface of the female rotor-side bore 11B is 285, so the female rotor-side maximum volume existence angle δf is 135. The product of the number of teeth Zf of the female rotor 1B minus the number of teeth Zm of the male rotor 1A (Zf - Zm) and the rotational angle range of the female rotor 1B corresponding to the circumferential width of the tooth grooves of the female rotor 1B (360 / Zf) is 90, thereby satisfying the condition of formula (1). Therefore, the suction completion timing of the male rotor-side working chamber 10A can be delayed from the reference timing, and the suction completion timing of the female rotor-side working chamber 10B can also be delayed from the reference timing.

[0023] First, the timing of completion of suction into the female rotor side working chamber 10B in this embodiment (in other words, the timing at which the closure portion 20 of the suction side casing 9 closes the suction port 14 for the female rotor side working chamber 10B) will be explained using Figure 5.

[0024] Figure 5 is a development view of the tooth portion 3B of the female rotor 1B, showing multiple female rotor-side working chambers 10B together with a portion of the suction port 14 in this embodiment. The vertical direction in Figure 5 is the axial direction of the tooth portion 3B of the female rotor 1B. The horizontal direction in Figure 5 is the circumferential direction of the tooth portion 3B of the female rotor 1B, and their positions are shown in terms of the rotation angle of the female rotor 1B (more specifically, the rotation angle is defined by the position of a line connecting the rotation center of the male rotor 1A and the rotation center of the female rotor 1B as 0). In Figure 5, multiple oblique lines indicate multiple tooth tips that define the multiple female rotor-side working chambers 10B, and hatched female rotor-side working chambers 10B indicate the suction-completed state.

[0025] In this embodiment, the timing for completing the intake of the female rotor side working chamber 10B is set later than the reference timing at which the volume of the female rotor side working chamber 10B reaches its maximum (in other words, the reference timing at which the volume of the female rotor side working chamber 10B changes from a state where it is not maximum to a state where it is maximum), and before the propagation time of the pressure wave propagating within the female rotor side working chamber 10B from the discharge side end face 18B to the suction side end face 19B of the teeth portion 3B of the female rotor 1B has elapsed.

[0026] When the leading tooth tip of the leading and trailing tooth tips that define the female rotor side working chamber 10B reaches the low-pressure side cusp 12 at the discharge side end face 18B of the tooth portion 3B of the female rotor 1B, a pressure wave (backflow) is generated that is reflected by the inner wall of the main casing 8 that faces the discharge side end face 18B of the tooth portion 3B of the female rotor 1B and heads toward the suction side end face 19B of the tooth portion 3B of the female rotor 1B. The propagation time of the pressure wave propagating from the discharge side end face 18B to the suction side end face 19B of the tooth portion 3B of the female rotor 1B can be calculated by dividing the tooth groove length Lf of the female rotor 1B by the sound speed a. Therefore, the rotation angle φLMTf of the female rotor 1B (hereinafter referred to as the female rotor side backflow limit angle φLMTf) through which the pressure wave travels from the discharge side end face 18B of the tooth portion 3B of the female rotor 1B until it reaches the suction side end face 19B, based on the position of the low-pressure side cusp 12, can be calculated using the following equation (2), where ωf is the angular velocity of the female rotor 1B: φLMTf=(Lf / a)×ωf (2)

[0027] As shown in Figure 5, the position of the low-pressure cusp 12 is used as a reference, and the rotation angle φDf of the female rotor at which suction into the female rotor working chamber 10B is completed is set at the position of the leading tooth tip on the discharge end face 18B of the teeth 3B of the female rotor 1B (hereinafter referred to as the female rotor suction completion angle φDf). The female rotor suction completion angle φDf is set smaller than the female rotor backflow limit angle φLMTf. As a result, the suction completion timing of the female rotor working chamber 10B is set before the propagation time (Lf / a) of the pressure wave propagating from the discharge end face 18B to the suction end face 19B of the teeth 3B of the female rotor 1B has elapsed within the female rotor working chamber 10B.

[0028] Next, the timing of completion of suction into the male rotor side working chamber 10A in this embodiment (in other words, the timing at which the closure portion 20 of the suction side casing 9 closes the suction port 14 for the male rotor side working chamber 10A) will be described with reference to FIG. 6.

[0029] Figure 6 is a development view of the tooth portion 3A of the male rotor 1A, showing multiple male rotor-side working chambers 10A together with a portion of the suction port 14 in this embodiment. The vertical direction in Figure 6 is the axial direction of the tooth portion 3A of the male rotor 1A. The horizontal direction in Figure 6 is the circumferential direction of the tooth portion 3A of the male rotor 1A, and their positions are shown in terms of the rotation angle of the male rotor 1A (more specifically, the rotation angle is defined by the position of the line connecting the rotation center of the male rotor 1A and the rotation center of the female rotor 1B as 0). In Figure 6, multiple oblique lines indicate multiple tooth tips that divide the multiple male rotor-side working chambers 10A, and hatched male rotor-side working chambers 10A indicate the suction-completed state.

[0030] In this embodiment, the timing for completing the intake of the male rotor side working chamber 10A is set later than the reference timing for the volume of the male rotor side working chamber 10A to reach its maximum (in other words, the reference timing for the volume of the male rotor side working chamber 10A to change from a state where it is not maximum to a state where it is maximum), and before the time for the pressure wave to propagate from the discharge side end face 18A to the suction side end face 19A of the tooth portion 3A of the male rotor 1A within the male rotor side working chamber 10A has elapsed. The details of this will be explained below.

[0031] When the leading tooth tip of the leading and trailing tooth tips that define the male rotor side working chamber 10A reaches the low-pressure side cusp 12 at the discharge side end face 18A of the toothing 3A of the male rotor 1A, a pressure wave (backflow) is generated that is reflected by the inner wall of the main casing 8 that faces the discharge side end face 18A of the toothing 3A of the male rotor 1A and moves toward the suction side end face 19A of the toothing 3A of the male rotor 1A. The propagation time of the pressure wave propagating from the discharge side end face 18A to the suction side end face 19A of the toothing 3A of the male rotor 1A can be calculated by dividing the tooth groove length Lm of the male rotor 1A by the speed of sound a. Therefore, using the position of the low-pressure side cusp 12 as a reference, the rotation angle φLMTm of the male rotor 1A that the pressure wave travels until it reaches the suction side end face 19A of the toothing 3A of the male rotor 1A (hereinafter referred to as the male rotor side backflow limit angle φLMTm) can be calculated using the following equation (3): In the formula, ωm is the angular velocity of the male rotor 1A. φLMTm=(Lm / a)×ωm (3)

[0032] As shown in Figure 6, the rotation angle φDm of the male rotor 1A at which suction into the male rotor side working chamber 10A is completed is assumed to be set at the position of the leading tooth tip on the discharge end face 18A of the tooth portion 3A of the male rotor 1A, using the position of the low-pressure side cusp 12 as a reference (hereinafter referred to as the male rotor side suction completion angle φDm). The male rotor side suction completion angle φDm is set to be smaller than the male rotor side backflow limit angle φLMTm. As a result, the suction completion timing of the male rotor side working chamber 10A is set to be before the propagation time (Lm / a) of the pressure wave propagating from the discharge end face 18A to the suction end face 19B of the tooth portion 3A of the male rotor 1A has elapsed within the male rotor side working chamber 10A.

[0033] As described above, in this embodiment, the suction completion timing for the female rotor-side working chamber 10B is set later than the reference timing and before the pressure wave propagation time (Lf / a) has elapsed. Furthermore, the suction completion timing for the male rotor-side working chamber 10A is set later than the reference timing and before the pressure wave propagation time (Lm / a) has elapsed. This allows the suction volume to be increased by the inertia of the intake gas compared to when the suction completion timings for the female rotor-side working chamber 10B and the male rotor-side working chamber 10A are not set later than the reference timing. Furthermore, unlike when the suction completion timings for the female rotor-side working chamber 10B and the male rotor-side working chamber 10A are set after the pressure wave propagation time has elapsed, the pressure wave is not discharged through the suction port 14, so a decrease in the suction volume can be avoided. Therefore, the suction volume can be increased even when the rotor wrap angle is small.

[0034] In the above embodiment, the suction completion timing of not only the female rotor side working chamber 10B but also the male rotor side working chamber 10A is set later than the reference timing and before the pressure wave propagation time has elapsed, but this is not limiting. Although the overall suction volume will be reduced compared to the above embodiment, the suction completion timing of the male rotor side working chamber 10A may be set after the pressure wave propagation time has elapsed, or it may be set to the same timing as or earlier than the reference timing.

[0035] 1A... male rotor, 1B... female rotor, 3A, 3B... teeth, 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 faces, 19A, 19B... suction side end faces

Claims

1. A screw compressor comprising: a male rotor having a toothed portion with a plurality of tooth grooves formed therein; a female rotor having a toothed portion with a plurality of tooth grooves formed therein and arranged to mesh with the male rotor; a plurality of male rotor side working chambers formed in the plurality of tooth grooves of the male rotor; and a plurality of female rotor side working chambers formed in the plurality of tooth grooves of the female rotor, wherein a rotation angle range of the female rotor in which one of the plurality of female rotor side working chambers has the largest volume is greater than the product of the number of teeth of the female rotor minus the number of teeth of the male rotor and the rotation angle range of the female rotor corresponding to the circumferential width of the tooth grooves of the female rotor, and the suction completion timing of the female rotor side working chamber is set later than a reference timing at which the volume of the female rotor side working chamber is maximized and before the propagation time of the pressure wave propagating within the female rotor side working chamber from the discharge side end face to the suction side end face of the tooth portion of the female rotor has elapsed.

2. A screw compressor as claimed in claim 1, characterized in that the timing of completion of suction into the male rotor side working chamber is set later than the reference timing at which the volume of the male rotor side working chamber is maximized and before the propagation time of the pressure wave propagating within the male rotor side working chamber from the discharge side end face to the suction side end face of the tooth portion of the male rotor has elapsed.

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