Patent Application
20190128264
The present invention relates to a screw compressor which compresses a gas such as air or a refrigerant gas, and more particularly, to a tooth profile suitable for enhancing an efficiency to achieve high performance by smoothly discharging the oil and rotating a rotor to reduce torque, in an oil-cooled screw compressor of a type in which oil is injected into an operation chamber in which a gas to be compressed is confined in a compression procedure.
Screw compressors are widely used as air compressors as air pressure sources and as refrigerant gas compressors for relatively large refrigeration air conditioning cycles. A geometric shape of a screw rotor, which can be said to be a heart of the screw compressors, has a great influence on performance, vibration noise, and reliability. In particular, a tooth profile defined as a contour shape in a cross section perpendicular to an axis of the rotor is an important characteristic for determining factors, various studies have been made for many years, and various tooth profiles have been proposed, verified and carried out.
For example, JP 2009-243325 A (Patent Document 1) discloses a tooth profile in which a vibration noise is small and a high performance can be achieved, using an involute curve or a circular arc having a center on a pitch circle at a specific position of the tooth profile. In addition, JP 2007-146659 A (Patent Document 2) discloses a method of providing an outer circumferential circular arc at a tooth tip of a male rotor to reduce leakage from a part between a male tooth tip and a bore surface of the casing.
Patent Document 1: JP 2009-243325 A
Patent Document 2: JP 2007-146659 A
Patent Document 1 aims to reduce internal leakage and maintain low noise. In addition, Patent Document 2 aims to increase a sealing effect of oil.
In contrast, concerning the high performance in the sense of improving energy efficiency in an oil-cooled screw compressor, it was found that the discharge resistance of oil is related as one of the factors of performance degradation. A relation between the tooth profile and the discharge resistance of oil is not disclosed in Patent Documents 1 and 2.
In the oil-cooled screw compressor, oil is injected into the operation chamber in the compression procedure of a gas to be compressed. The oil has three functions. A first function is a lubricant that helps the rotation transmission due to contact between the female and male rotors, a second function is a sealant that reduces the internal leakage of the gas to be compressed for filling the gap between the rotors, and a third function is a coolant for the gas to be compressed which increases in temperature by compression. There is an oil that is used because of a high useful aspect, but density and viscosity are several hundred to several thousand times as much as the gas to be compressed. Therefore, when passing through a small cross-sectional area, resistance of a completely different order of magnitude compared to the gas to be compressed is generated. Here, the flow path having the smallest cross-sectional area through which the oil passes is an opening portion of the discharge port just before the operation chamber disappears.
There is another important phenomenon. The operating principle of the screw compressor is to move the operation chamber in an axial direction by rotating both rotors. Although the gas to be compressed and oil are mixed in the operation chamber, oils that are not uniformly distributed and have a high density are likely to accumulate at corner of the rear side. Therefore, when the compression is completed and the discharge port opens, the gas to be compressed on the front side is discharged first, whereas the oil tends to remain to the last.
Just before the operation chamber disappears, since most of the fluid left in the operation chamber becomes oil and the opening area of the discharge port decreases, the discharge resistance significantly increases. Although the discharge resistance is large, since the volume of the operation chamber decreases, the internal pressure of the operation chamber rises. This high pressure acts on the tooth surface of the rotor, which causes an increase in the torque for driving the rotor.
Since this phenomenon occurs every time at the period of the meshing of the rotors at the timing just before the operation chamber disappears, an increase in the drive torque of the screw compressor is caused, and in the case of electric motor, the power consumption of the motor is increased. That is, the discharge resistance of the oil causes extra energy consumption, which is one cause of performance degradation.
In view of the above circumstances, an object of the oil-cooled screw compressor of the present invention is to reduce the driving resistance of the rotor by reducing the discharge resistance of oil and to improve the energy efficiency, that is, the performance.
In order to solve the above-mentioned problems, the present invention provides, for example, an oil-cooled screw compressor including: a screw rotor which has a pair of a male rotor and a female rotor rotating by meshing with each other around two parallel axes and each having twisted teeth, and in which most of teeth of the male rotor are located outside a male pitch circle centered on the axis of the male rotor in a cross section perpendicular to the axis of the male rotor, and most of teeth of the female rotor are located inside a female pitch circle centered on the axis of the female rotor in the cross section perpendicular to the axis of the female rotor; and a casing which has a bore including two cylindrical holes which partly overlap and have the same length to accommodate the pair of the male rotor and the female rotor, and in which an end surface of the bore is a bore end surface that faces in parallel with end surfaces of the pair of the male rotor and the female rotor at a slight gap, the casing being provided with an oil injection port in at least one of operation chambers formed by being surrounded with tooth grooves of the pair of the male rotor and the female rotor meshing with each other and the bore accommodating the tooth grooves, and the bore end surface being provided with an opening portion serving as a discharge port which discharges oil injected together with a gas to be compressed, in which a tooth profile curve representing a contour shape of the screw rotor on a cross section perpendicular to the axis of the screw rotor has only a finite length of a section having a maximum radius in the male rotor, the section is a circular arc, a center of the circular arc coincides with the center of the male rotor tooth profile, the tooth profile curve has only a finite length of a section having a minimum radius in the female rotor, the section is a circular arc, a center of the circular arc coincides with the center of the female rotor tooth profile, a ratio of an opening angle of the circular arc which is the finite section of the male rotor to an opening angle of the circular arc which is the finite section of the female rotor is equal to a ratio of the number of teeth of the female rotor to the number of teeth of the male rotor, a contour shape on a discharge side bore end surface of the discharge port sets a position at which a tooth tip of the male rotor passes on a line segment connecting respective rotation centers which are the axes of the pair of the male rotor and the female rotor, as a base point, a contour line extending from the base point to the male rotor side is located on a locus line when the tooth tip of the male rotor facing the base point is reversely rotated or to be closer to the center of the male rotor tooth profile than the locus line, and the contour line extending from the base point to the female rotor side is located on the locus line when the tooth base of the female rotor is reversely rotated or to be closer to the center of the female rotor tooth profile than the locus line.
According to the present invention, it is possible to provide an oil-cooled screw compressor that reduces the torque for driving the rotor by reducing discharge resistance of oil and improves energy efficiency.
An embodiment of the present invention will be described with reference to
The oil-cooled screw compressor includes a screw rotor which has a pair of a male rotor 1 and a female rotor 2 rotating by meshing with each other around parallel two axes and each having twisted teeth, and in which most of teeth of the male rotor 1 are located outside a male pitch circle centered on the axis of the male rotor 1 in a cross section perpendicular to the axis of the male rotor 1, and most of teeth of the female rotor 2 are located outside the male pitch circle centered on the axis of the male rotor 1 in the cross section perpendicular to the axis of the female rotor 2; and a casing 3 which has a bore 4 including two cylindrical holes which partly overlap and have the same length to accommodate the pair of rotors, and in which an end surface of the bore 4 is a bore end surface that faces in parallel with end surfaces of the pair of rotors at a slight gap, and the casing 3 is provided with an oil injection port 7 in at least one of operation chambers formed by being surrounded with tooth grooves of a pair of rotors meshing with each other and the bore 4 accommodating the tooth grooves, and the bore end surface is provided with a discharge port which discharges the oil injected together with a gas to be compressed. Here, in the male pitch circle and the female pitch circle, a point obtained by dividing a line segment connecting the rotation center of the male rotor and the rotation center of the female rotor by a ratio of the number of teeth of the male rotor and the number of teeth of the female rotor is called a pitch point P, a circle in which a distance from the rotation center of the male rotor to the pitch point P is a radius is called a male pitch circle, and a circle in which a distance from the rotation center of the female rotor to the pitch point P is a radius is called a female pitch circle.
The male rotor 1 and the female rotor 2 rotate, while meshing with each other in the respective cylindrical holes. A tooth profile is geometrically designed for the meshing part between the male rotor 1 and the female rotor 2 to theoretically have a gap of 0, an appropriate gap is set in the tooth profile to allow thermal deformation, gas pressure deformation, vibration and machining error, and the meshing part is manufactured to be thinner by that amount. Since the essence of the present invention does not directly participate in the setting method of the gap, although the existence of the gap is added to the consideration, the tooth profile described in this embodiment is geometrically designed and described a gap as 0. Therefore, even if expressed as “contact” in the sentence, there are many cases where a minute gap exists between the actual tooth profiles.
Regarding the direction in which the screw compressor is installed, unlike the direction illustrated in
When the opening angle and the number of teeth of these female and male rotors satisfy the following formula (1), continuous meshing of the female and male rotor is established.
θm: θf=Zf: Zm (1)
Since the curve on the rear side (front and rear of the tooth profile means front and rear with respect to the rotational direction) of the rear tooth tip point 11 of the male rotor 1 is not essence of the present invention, a retreating surface of the tooth profile of the Patent Document 1 is used. As the curve on the front side of the front tooth tip point 12, the advancing surface of Patent Document 1 is used. However, when the tooth profile of the male rotor 1 is reversely rotated by 6 degrees from the reference and the rotation angle is set to minus 6 degrees and the front tooth tip point 12 is on a line segment connecting the rotation centers 23 and 13 of the female and male rotors, a shape connecting the curves of the advancing surface of Patent Document 1 to the front side from the point 12 is obtained. Thus, a smooth continuous tooth profile can be formed at the front tooth tip point 12.
The tooth profile curve of the retreating surface of the female rotor of Patent Document 1 is used as a curve after the rear tooth base point 21 of the female rotor 2, and the tooth profile curve of the advancing surface of the female rotor of Patent Document 1 is used as the curve on the front side of the front tooth base point 22. As for the front side, like the male rotor 1, when the female rotor is reversely rotated by 4 degrees from the reference and the front tooth base point 22 is set to a position aligned with the line connecting the rotation centers 23 and 13 of the female and male rotors, a shape which connects the curve of the advancing surface of Patent Document 1 to the front side from the front tooth base point 22 is obtained.
In tooth profile of the conventional female rotor, except for the tooth profile of Patent Document 2, the portions near the tooth tip at both ends of the tooth are convex curves, and the vicinity of the center between them is a concave curve. In contrast, as a feature of the tooth profile of the female rotor 2 according to this embodiment, since the section 21 to 22 of the tooth base circle in the vicinity of the center of the tooth profile are convex, both sides thereof are concave, and both end portions which are outside thereof are convex.
A contour shape of the discharge port 6 is adapted to the tooth profile. The inside of the contour line is an opening portion which opens to the discharge side bore end surface as the discharge port. The drawing is divided, by the line segment connecting the rotation center 13 of the male rotor and the rotation center 23 of the female rotor, into an upper half region and a lower half region which are opposite to the rotation direction, but the discharge port 6 opens to the lower half region. When both rotors are at the reference position of 0 degree, the rear tooth tip point 11 of the male rotor and the rear tooth base point 21 of the female rotor are in contact with each other, but the position facing the contact point is set as a base point of the contour line of the discharge port 6. Further, the term “facing” means that it is at a position in which the rear tooth tip point and the rear tooth base point are in close contact with each other with the gap between the rotor end surface and the bore end surface being sandwiched therebetween, and in
The contour line extending from the base point to the right side matches the locus traced by the rear tooth tip point 11 when the male rotor 1 is reversely rotated from the reference position. Alternatively, it is a line slightly shifted from the locus thereof, for example, within 3% of the radius of the male rotor to a line shifted toward the rotation center 13 of the male rotor. Similarly, the left side from the base point is set to a locus traced by the rear tooth base point 21 when the female rotor 2 is reversely rotated from the reference position, or to be closer to the rotation center 23 of the female rotor slightly smaller than the locus line, for example, within 3% of the female rotor radius. Therefore, the right and left lines are close to each other just below the base point, and the width thereof is about the width of the tool such as the end mill for processing the discharge port 6.
When the male rotor 1 and the female rotor 2, which are three-dimensional bodies, are meshed with both the conventional tooth profile and the tooth profile of the present embodiment, both rotors are brought into contact with one continuous line. This line is called a seal line and is three-dimensionally bent and has the role of partitioning the operation chamber which can be located on the upper side of the rotor and the operation chamber which can be located on the lower side. Although the seal line is formed between both rotors, it cannot be visually observed, but as seen from the right side of
In each of the operation chambers 31 to 37 of the screw compressor, one tooth groove of each of both female and male rotors communicates with each other, and the outer circumference and the end surface thereof are formed by being closed with the bore 4 which is the inner surface of the casing. When the rotor is rotated, the operation chamber moves parallel to the axial direction from the suction side end to the discharge side end. Due to the parallel movement, since the internal volume of the operation chamber gradually decreases, the internal gas to be compressed is compressed. When pressure rises to a predetermined pressure, it communicates with the discharge port 6 which is a penetration hole opened at the bore end on the discharge side, and the gas to be compressed and the oil are discharged to outside of the bore. When the rear end of the operation chamber reaches the discharge end, the internal volume becomes 0, and the discharging is completed. The shape near the rear end of the operation chamber is determined by the tooth profile of the rotor. In the operation chamber of the rotor according to the present embodiment, the upper half region is eliminated first, and the lower half region remains to the last.
The shape of the seal line 30 is determined by the tooth profile, but the feature of the seal line according to this embodiment is the shape of the rear end of the operation chamber. The seal line 30 is bent, a portion 41 extending under the seal line extending long downward in the right direction is a boundary, and divides the left and right operation chambers (for example, the operation chambers 35 and 36). That is, the portion 41 extending under the seal line has a shape in which the lower half region extends toward the suction side with respect to the upper half region when the contour of the operation chamber is viewed from the rotor side surface. At the rear end (the left end in
The right side of the step is a position at which the front tooth tip point 12 and the front tooth base point 22 are in contact with each other, and at that time, a certain range of the advancing surface simultaneously comes into contact with each other. Therefore, in
Since the internal volume gradually expands in the operation chambers 31 to 33 in which the upper side of the seal line 30 is in the suction process, the gas to be compressed flowing in from the suction port 5 opened in the casing 3 is suctioned therein. The operation chambers 34 to 37 in the compression process and the discharging process are arranged on the lower side of the seal line 30. The volumes of these operation chambers are gradually reduced.
The operation chamber is a space in which the teeth grooves of both rotors (because the male rotor is the space formed between the teeth and the adjacent teeth, and the female rotor is a concave tooth, it is a space surrounded by the teeth) communicates one by one with each other to form a V shape. The outer side of the operation chamber is closed by the inner surface and the end surface of the bore 4 of the casing 3, and since the space between the rotors 1 and 2 is blocked by the seal line 30, a closed space is formed. As mentioned above, since a minute gap for smoothly rotating the rotor is present between both rotors or between the rotor and the bore, there is a slight internal leakage of gas to be compressed or oil, but it is not directly related to the essence of this embodiment.
When both rotors 1 and 2 are rotated while being meshed with each other, the operation chambers 31 to 37 move to the right side from the suction side end to the discharge side end like the rotary advertisement tower of the barbershop. In
Although it is the oil injected into the operation chamber 34, since the oil has a density of much higher than the gas to be compressed and is injected at a speed slower than the movement speed of the operation chamber, the oil tends to accumulate at the rear end of the operation chamber. Therefore, the oil moves so as to be scraped by the rotor at the rear end of each operation chamber. Even in the discharging process, even if the operation chamber moving relative to the discharge port 6 opens, the rate at which the gas to be compressed is discharged is high at the initial stage, and most of the oil is discharged at the last stage.
Since the opening area of the discharge port decreases at the final stage of the discharging process, troubles of increasing discharge resistance tend to occur. This will be described in detail with reference to
The contour line of the discharge port 6 illustrated in
In addition, for comparison,
Further,
The final stage of the discharging process will be described with time with reference to
For comparison, the final stage of the same discharge in the conventional example will be described with reference to
In this way, in the conventional tooth profile, despite the fact that the discharge resistance is larger than this embodiment, since the operation chamber surely reduces the volume, the pressure of the inside oil inevitably rises sharply. The pressure acts on the rotor tooth surface and leads to an increase in torque for driving the rotor. Although the area in which the oil pressure acts is small, the energy loss exceeds the measurement error or negligible level due to the high pressure.
In contrast, according to this embodiment, the operation chamber just before disappearance exists only in the lower half region from the line connecting the centers of the female and male teeth shapes, and the opening area with respect to the operation chamber volume increases. This makes it possible to smoothly discharge the oil and to prevent a sudden rise in the internal pressure of the operation chamber just before disappearance. Therefore, since the torque for driving the rotor can be reduced, and the power consumption of the motor that gives rotation and the fuel consumption of the engine can be reduced, it is possible to achieve an oil-cooled screw compressor with high energy efficiency and excellent energy saving.
Incidentally, in the shape of the contour line, the range not defined herein is not concerned with “smooth discharge of oil just before the disappearance of the operation chamber” which is the essence of the present invention.
Although the embodiments have been described above, the present invention is not limited to the embodiments described above, but includes various modifications. For example, the above-described embodiments have been described in detail in order to describe the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-083707 | Apr 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/013297 | 3/30/2017 | WO | 00 |
