The present invention relates to a screw pump that draws fluid into a housing and discharges the fluid to the exterior of the housing by rotating a pair of screw rotors. The present invention further relates to screw rotors in a screw pump.
Patent Document 1 discloses a screw pump that has a pair of screw rotors engaged with each other. As the screw rotors rotate, the screw pump operates to transport fluid.
As shown in
The cross section of the tooth profile of the second conventional screw rotor 90B perpendicular to the rotor axis includes a tooth top arc Q2R2, a tooth bottom arc S2T2, a first curve S2Q2, and a second curve T2R2. The first curve S2Q2 connects a first end S2 of the tooth bottom arc S2T2 to a first end Q2 of the tooth top arc Q2R2. The second curve T2R2 connects a second end T2 of the tooth bottom arc S2T2 to a second end R2 of the tooth top arc Q2R2.
The first curve S1Q1 of the first conventional screw rotor 90A includes a trochoidal curve U1S1 and a connecting portion Q1U1. The trochoidal curve U1S1 is created by the path of the first end Q2 of the tooth top arc Q2R2 when the second conventional screw rotor 90B revolves about the first conventional screw rotor 90A. The connecting portion Q1U1 is a straight line that connects an end U1 of the trochoidal curve U1S1 to the first end Q1 of the tooth top arc Q1R1. The second curve T1R1 includes an outer circular arc R1W1, an involute curve W1Y1, and an inner circular arc Y1T1. The involute curve W1Y1 is located between the outer circular arc R1W1 and the inner circular arc Y1T1. The outer circular arc R1W1 is connected to the tooth top arc Q1R1 and the inner circular arc Y1T1 is connected to the tooth bottom arc S1T1.
Similarly, the first curve S2Q2 of the second conventional screw rotor 90B includes a trochoidal curve U2S2 and a connecting portion Q2U2, which is a straight line. The second curve T2R2 includes an outer circular arc R2W2, an involute curve W2Y2, and an inner circular arc Y2T2.
Neither the first conventional screw rotor 90A nor the second conventional screw rotor 90B contacts the housing of the screw pump. Further, the first conventional screw rotor 90A and the second conventional screw rotor 90B do not contact each other. Such arrangement thus may potentially cause leakage of the fluid (leakage of gas). Although the tooth profiles of the first and second conventional screw rotors 90A, 90B are shaped in such a manner as to suppress the fluid leakage, the fluid leakage is desired to be suppressed further effectively.
Accordingly, it is an objective of the present invention to provide a screw pump and a screw rotor that reliably suppress leakage of fluid.
In order to achieve the foregoing objective and in accordance with one aspect of the present invention, a screw pump including a housing, and a first screw rotor and a second screw rotor received in the housing is provided. The first screw rotor and the second screw rotor rotate in a direction in which the first and second screw rotors become engaged with each other. A fluid is drawn into the housing and then discharged to the exterior through rotation of the first screw rotor and the second screw rotor. A cross section of a tooth profile of the first screw rotor and a cross section of a tooth profile of the second screw rotor perpendicular to the respective rotor axes each include a first circular arc portion, a second circular arc portion, a first curved portion, and a second curved portion. The first circular arc portion and the second circular arc portion each have a first end and a second end. The radius of curvature of the second circular arc portion is smaller than the radius of curvature of the first circular arc portion. The first curved portion connects the first end of the first circular arc portion to the first end of the second circular arc portion. The second curved portion connects the second end of the first circular arc portion to the second end of the second circular arc portion. The first curved portion of the first screw rotor is a first trochoidal curve created by the first end of the first circular arc portion of the second screw rotor. The second curved portion of the first screw rotor includes an involute curve and a second trochoidal curve that extend continuously from each other. The involute curve extends continuously from the second end of the first circular arc portion of the first screw rotor. The second trochoidal curve is created by the second end of the first circular arc portion of the second screw rotor. The first curved portion of the second screw rotor is a first trochoidal curve created by the first end of the first circular arc portion of the first screw rotor. The second curved portion of the second screw rotor includes an involute curve and a second trochoidal curve that extend continuously from each other. The involute curve extends continuously from the second end of the first circular arc portion of the second screw rotor. The second trochoidal curve is created by the second end of the first circular arc portion of the first screw rotor.
The rotary axis of the first screw rotor can be referred to as a first axis, and the rotary axis of the second screw rotor can be referred to as a second axis. The angle of the first circular arc portion of the first screw rotor with respect to the first axis, the angle of the second circular arc portion of the first screw rotor with respect to the first axis, the angle of the first circular arc portion of the second screw rotor with respect to the second axis, and the angle of the second circular arc portion of the second screw rotor with respect to the second axis can all be set equal.
In accordance with another aspect of the present invention, a screw rotor of a screw pump is provided. The screw rotor is one of a first screw rotor and a second screw rotor.
The term “a cross section of the tooth profile of a first screw rotor perpendicular to the rotor axis” refers to a cross-sectional shape of the tooth profile of the first screw rotor on an imaginary plane extending perpendicular to the rotary axis of the first screw rotor. The term “a cross section of a second screw rotor perpendicular to the rotor axis” refers to a cross-sectional shape of the tooth profile of the second screw rotor on an imaginary plane extending perpendicular to the rotary axis of the second screw rotor. The tooth profile according to the present invention increases the axial dimension (the dimension along the rotary axis) of a tooth top surface. The tooth top surface is a circumferential surface formed by a first circular arc portion. A tooth bottom surface is a circumferential surface formed by the second circular arc portion. The increased axial dimension of the tooth top surface decreases the amount of the fluid leaking from between a housing and the tooth top surface.
a) is a cross-sectional view taken along line A-A of
b) is a cross-sectional view showing a first screw rotor and a second screw rotor in a state rotated by 180° from the state in
c) is an enlarged view showing a portion of
a) is a diagrammatic view showing the first curved portions that are engaged with each other;
b) is an enlarged view showing the second curved portions that are engaged with each other;
a), 9(b), and 9(c) are cross-sectional views perpendicular to the axes of the rotors, showing examples of a tooth profile of a first screw rotor and a tooth profile of a second screw rotor;
d), 9(e), and 9(f) are cross-sectional views showing comparative examples of a tooth profile of a first conventional screw rotor and a tooth profile of a second conventional screw rotor, as viewed perpendicularly to the axes of the rotors;
a) is a cross-sectional view showing a tooth profile of a first screw rotor and a tooth profile of a second screw rotor according to a second embodiment of the present invention;
b) is a cross-sectional view showing a portion of
The first cylindrical portion 160 has a first support hole 190 and the second cylindrical portion 161 has a second support hole 191. The first support hole 190 and the second support hole 191 each extend through the shaft receiving body 15. A drive shaft 20 is received in the first support hole 190 and a driven shaft 21 is arranged in the second support hole 191. A pair of first roller bearings 240 support the drive shaft 20 in a manner rotatable with respect to the shaft receiving body 15. A pair of second roller bearings 241 support the driven shaft 21 in a manner rotatable with respect to the shaft receiving body 15. The axis of the first cylindrical portion 160 coincides with a first axis 171, which is the rotary axis of the drive shaft 20. The axis of the second cylindrical portion 161 coincides with a second axis 181, which is the rotary axis of the driven shaft 21. The front end of the drive shaft 20 and the front end of the driven shaft 21 (left end as viewed in
The rotor housing member 12 accommodates a first screw rotor 17 and a second screw rotor 18. The front end (left end as viewed in
The first screw rotor 17 is rotated in a first rotational direction X and the second screw rotor 18 is rotated in a second rotational direction Z. The first rotational direction X and the second rotational direction Z are opposite to each other. In
The first screw rotor 17 and the second screw rotor 18 are screw gears each serving as a fluid transport body. Specifically, a drive tooth 17A is formed in the first screw rotor 17 and a driven tooth 18A is provided in the second screw rotor 18. The first screw rotor 17 includes a drive screw groove 17a, which extends between adjacent portions of the drive tooth 17A. The second screw rotor 18 includes a driven screw groove 18a, which extends between adjacent portions of the driven tooth 18A. The axial direction of the first screw rotor 17 is to the direction of the first axis 171, which is the rotary axis of the first screw rotor 17. The axial direction of the second screw rotor 18 is to the direction of the second axis 181, which is the rotary axis of the second screw rotor 18.
The first screw rotor 17 and the second screw rotor 18 are received in the rotor housing member 12 in such a manner that the drive tooth 17A and the driven tooth 18A are arranged in the driven screw groove 18a and the drive screw groove 17a, respectively. In other words, the first screw rotor 17 and the second screw rotor 18 are configured in such a manner as to provide a sealed space between the screw rotors 17, 18. Pump chambers 10 each shaped like a figure eight are defined between each of the first and second screw rotors 17, 18 and an inner circumferential surface 121 of the rotor housing member 12.
The thickness of the drive tooth 17A decreases gradually from the front end (left end as viewed in
A gear housing member 22 having a lidded cylindrical shape is joined with and fixed to the rear end of the rear housing member 14. A rear end 20a of the drive shaft 20 and a rear end 21a of the driven shaft 21 (right end as viewed in
An inlet port 28 is defined in the center of the front housing member 13. An outlet port 29 is provided in the rear end of the rotor housing member 12. The inlet port 28 and the outlet port 29 each communicate with the pump chambers 10.
As the electric motor 26 runs, the drive shaft 20 is rotated through the output shaft 26a and the shaft coupling 27. This causes the driven shaft 21 to rotate in the direction different from the rotational direction of the drive shaft 20 through engagement and connection between the two timing gears 25. In other words, the first screw rotor 17 and the second screw rotor 18 also rotate, drawing gas into the pump chambers 10 through the inlet port 28. The gas is then sent to the outlet port 29 and discharged to the exterior of the pump chambers 10 through the outlet port 29.
The tooth profile of the first screw rotor 17 and that of the second screw rotor 18 will hereafter be explained in detail.
With reference to
The cross section of the tooth profile of the first screw rotor 17 perpendicular to the rotor axis includes a drive tooth top arc A1B1, a drive tooth bottom arc C1D1, a first drive curve A1C1, and a second drive curve B1D1. The drive tooth top arc A1B1 is a first circular arc portion extending from a first end A1 to a second end B1 about the first midpoint P1. The drive tooth bottom arc C1D1 is a second circular arc portion extending from a first end C1 to a second end D1 about the first midpoint P1. The first drive curve A1C1 is a first curved portion that connects the first end A1 of the drive tooth top arc A1B1 to the first end C1 of the drive tooth bottom arc C1D1. The second drive curve B1D1 is a second curved portion that connects the second end B1 of the drive tooth top arc A1B1 to the second end D1 of the drive tooth bottom arc C1D1.
The first midpoint P1 is arranged between the drive tooth top arc A1B1 and the drive tooth bottom arc C1D1. The first end A1 and the first end C1 are located on the same side (left side as viewed in
With reference to
The second midpoint P2 is arranged between the driven tooth top arc A2B2 and the driven tooth bottom arc C2D2. The first end A2 and the first end C2 are located on the same side (right side as viewed in
The second drive curve B1D1 is a composite curve formed by a drive involute curve B1E1 and a second drive trochoidal curve E1D1 that extend continuously from each other at a first intersection point E1. The drive involute curve B1E1 extends continuously from the second end B1 of the drive tooth top arc A1B1. The second drive trochoidal curve E1D1 extends continuously from the second end D1 of the drive tooth bottom arc C1D1.
Similarly, the second driven curve B2D2 is a composite curve formed by a driven involute curve B2E2 and a second driven trochoidal curve E2D2 that extend continuously from each other at a second intersection point E2. The driven involute curve B2E2 extends continuously from the second end B2 of the driven tooth top arc A2B2. The second driven trochoidal curve E2D2 extends continuously from the second end D2 of the driven tooth bottom arc C2D2.
The drive involute curve B1E1 is defined by a first base circle Co1, which is illustrated in
The second drive trochoidal curve E1D1 is created by the path of the second end B2 of the driven tooth top arc A2B2. The second driven trochoidal curve E2D2 is created by the path of the second end B1 of the drive tooth top arc A1B1.
As illustrated in
As shown in
Similarly, the second screw rotor 18 has a driven tooth top surface 182, which is the tooth top surface of the driven tooth 18A, and a driven tooth bottom surface 183, which is the tooth bottom surface of the driven screw groove 18a. A cross section of the driven tooth top surface 182 perpendicular to the rotor axis is the driven tooth top arc A2B2. A cross section of the driven tooth bottom surface 183 perpendicular to the rotor axis is the driven tooth bottom arc C2D2. The driven tooth top surface 182 and the driven tooth bottom surface 183 are circumferential surfaces that extend spirally along the second axis 181.
If the first angle θ1 of the first screw rotor 17 is equal to the second angle θ2, the axial dimension of the drive tooth top surface 172 is substantially equal to the axial dimension of the drive tooth bottom surface 173. If the first angle θ1 of the second screw rotor 18 is equal to the second angle θ2, the axial dimension of the driven tooth top surface 182 is substantially equal to the axial dimension of the driven tooth bottom surface 183. The axial dimension of the drive tooth top surface 172 is a dimension measured along the first axis 171 and the axial dimension of the driven tooth top surface 182 is a dimension measured along the second axis 181.
As illustrated in
With reference to
The angle between the inner circumferential surface 121 of the rotor housing member 12 and the driven tooth side surface 184 is a second clearance angle δ. The drive tooth top angle α is an obtuse angle (an angle greater than 90° and smaller than 180°) and the first clearance angle γ is an acute angle (an angle less than 90°). The driven tooth top angle β is an obtuse angle and the second clearance angle δ is an acute angle. In the first embodiment, the drive tooth top angle α is equal to the driven tooth top angle β (α=β). The first clearance angle γ is equal to the second clearance angle δ (γ=δ).
A procedure for forming the cross section of the tooth profile of the first screw rotor 17 perpendicular to the rotor axis and the cross section of the tooth profile of the second screw rotor 18 perpendicular to the rotor axis will now be explained.
First, as illustrated in
Then, the first outer circle C11 having an outer radius R1 greater than the pitch radius r and the first inner circle C21 with an inner radius R2 smaller than the pitch radius r are determined with respect to the first midpoint P1 (R2≦r≦R1). Similarly, the second outer circle C12 with the outer radius R1 and the second inner circle C22 with the inner radius R2 are determined with respect to the second midpoint P2. The inter-pitch distance L is the sum of the outer radius R1 and the inner radius R2 (L=R1+R2=2r).
Subsequently, with reference to
Next, as illustrated in
Similarly, with reference to
The imaginary straight line M including the first midpoint P1 and the second midpoint P2 is then determined as illustrated in
As illustrated in
Similarly, with reference to
The portion of the first outer circle C11 between the first end A1 and the second end B1 forms the drive tooth top arc A1B1. The drive tooth top arc A1B1 is determined in such a manner that an acute angle is formed between the drive tooth top arc A1B1 and the first drive curve A1C1. The portion of the first inner circle C21 between the first end C1 and the second end D1 forms the drive tooth bottom arc C1D1. The drive tooth bottom arc C1D1 is determined in such a manner that the first midpoint P1 is provided between the drive tooth top arc A1B1 and the drive tooth bottom arc C1D1. The radius of curvature of the drive tooth top arc A1B1 is the outer radius R1 and the radius of curvature of the drive tooth bottom arc C1D1 is the inner radius R2.
In the same manner, the portion of the second outer circle C12 between the first end A2 and the second end B2 forms the driven tooth top arc A2B2. The driven tooth top arc A2B2 is determined in such a manner that an acute angle is formed between the driven tooth top arc A2B2 and the first driven curve A2C2. The portion of the second inner circle C22 between the first end C2 and the second end D2 forms the driven tooth bottom arc C2D2. The driven tooth bottom arc C2D2 is determined in such a manner that the second midpoint P2 is provided between the driven tooth top arc A2B2 and the driven tooth bottom arc C2D2.
In this manner, the procedure for forming the cross sections of the tooth profiles of the first screw rotor 17 and the second screw rotor 18 perpendicular to the respective rotor axes is accomplished.
As the first screw rotor 17 of the screw pump 11 continuously rotates in the first rotational direction X and the second screw rotor 18 continuously rotates in the second rotational direction Z, the first end A2 of the second screw rotor 18 moves along the first drive curve A1C1, as illustrated in
As the first screw rotor 17 and the second screw rotor 18 continuously rotate, the second end B1 of the first screw rotor 17 moves along the second driven trochoidal curve E2D2. The drive involute curve B1E1 then becomes engaged with the driven involute curve B2E2. Afterwards, with reference to
a),
In
In the first example shown in
In the second example shown in
In the third example shown in
As is clear from comparison between the first example of
As is clear from comparison between the second example of
As is clear from comparison between the third example of
In other words, when the involute radius Ro is smaller than the pitch radius r (Ro<r), the values θ1 and θ2 of the first and second screw rotors 17, 18 are greater than the values θ1 and θ2 of the first and second conventional screw rotors 90A, 90B. When the involute radius Ro is greater than or equal to the pitch radius r (r≦Ro), the drive involute curve B1E1 is not engaged with the driven involute curve B2E2.
The first embodiment has the following advantages.
(1) The second drive curve B1D1 is the composite curve formed by the drive involute curve B1E1 and the second drive trochoidal curve E1D1. The second driven curve B2D2 is the composite curve formed by the driven involute curve B2E2 and the second driven trochoidal curve E2D2. In contrast, a second conventional drive curve T1R1, which is illustrated in
As the circumferential dimension of the drive tooth top arc A1B1 increases, the axial dimension of the drive tooth top surface 172 increases. This increases the seal length between the drive tooth top surface 172 and the inner circumferential surface 121 of the rotor housing member 12. Thus, leakage of fluid between adjacent ones of the pump chambers 10 is effectively suppressed. Further, as the circumferential dimension of the driven tooth top arc A2B2 increases, the axial dimension of the driven tooth top surface 182 increases. The seal length between the driven tooth top surface 182 and the inner circumferential surface 121 of the rotor housing member 12 is thus increased. This effectively suppresses the leakage of the fluid between adjacent ones of the pump chambers 10.
(2) As the circumferential dimension of the drive tooth bottom arc C1D1 increases, the axial dimension of the drive tooth bottom surface 173 increases. This facilitates machining of the drive screw groove 17a. Also, as the circumferential dimension of the driven tooth bottom arc C2D2 increases, the axial dimension of the driven tooth bottom surface 183 increases. This facilitates machining of the driven screw groove 18a.
(3) The drive tooth side surface 174 of the first screw rotor 17 is opposed to the driven tooth side surface 184 of the second screw rotor 18. The angle between the drive tooth side surface 174 and the drive tooth top surface 172 is the drive tooth top angle α. The angle between the driven tooth side surface 184 and the driven tooth top surface 182 is the driven tooth top angle β. The drive tooth side surface 174 of the first screw rotor 17 is created by the second driven curve B2D2, which is the composite curve formed by the driven involute curve B2E2 and the second driven trochoidal curve E2D2. In contrast, the drive tooth side surface of the first conventional screw rotor 90A, which is shown in
Similarly, the driven tooth side surface 184 of the second screw rotor 18 is created by the second drive curve B1D1, which is the composite curve formed by the drive involute curve B1E1 and the second drive trochoidal curve E1D1. In contrast, the driven tooth side surface of the second conventional screw rotor 90B, which is shown in
(4) The second driven curve B2D2, which is the composite curve formed by the driven involute curve B2E2 and the second driven trochoidal curve E2D2, forms the drive tooth side surface 174. The second drive curve B1D1, which is the composite curve formed by the drive involute curve B1E1 and the second drive trochoidal curve E1D1, forms the driven tooth side surface 184. This enlarges the clearance around the linear seal portion created between the drive tooth side surface 174 and the driven tooth side surface 184 in the vicinity of the drive tooth bottom surface 173 and the vicinity of the driven tooth bottom surface 183. Thus, the screw pump 11 is further effectively prevented from catching foreign objects.
For example, the involute curve W1Y1 illustrated in
The first embodiment may be modified as follows.
The thickness (the axial dimension) of the drive tooth 17A may be uniform from the front end to the rear end of the first screw rotor 17, instead of decreasing from the front end to the rear end of the first screw rotor 17. Similarly, the thickness of the driven tooth 18A may be uniform from the front end to the rear end of the second screw rotor 18.
The number of the drive teeth 17A of the first screw rotor 17 and the number of the driven teeth 18A of the second screw rotor 18 are not restricted to one but may be two.
The first angle θ1 and the second angle θ2 may be altered as needed. For example, as in a second embodiment shown in
Number | Date | Country | Kind |
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2006-240042 | Sep 2006 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2007/067125 | 9/3/2007 | WO | 00 | 3/26/2008 |