Patent Application
20120003113
The present invention relates to measures to improve efficiency of screw compressors.
Screw compressors have been used as compressors for compressing a refrigerant or air. For example, Patent Document 1 discloses a single screw compressor including a screw rotor, and two gate rotors.
The single screw compressor will be described below. The screw rotor is substantially in the shape of a column, and a plurality of helical grooves are formed in an outer peripheral surface thereof. The screw rotor is contained in a casing. The helical grooves of the screw rotor constitute fluid chambers. Each of the gate rotors is substantially in the shape of a flat plate. The gate rotor includes a plurality of rectangular plate-shaped gates which are radially arranged. The gates of the gate rotor mesh with the helical grooves of the screw rotor. When the screw rotor is rotated, the gates move relatively from the start ends (ends through which the fluid is sucked) to terminal ends (ends through which the fluid is discharged) of the helical grooves, and the fluid is sucked into the fluid chambers for compression.
A screw compressor disclosed by Patent Document 2 includes a lubrication passage for supplying lubricant oil to the fluid chambers. In the screw compressor disclosed by Patent Document 2, a sump for collecting the lubricant oil is formed in the casing, and the lubricant oil in the sump is supplied to the fluid chambers due to difference in pressure between the sump and the fluid chamber. The lubricant oil supplied to the fluid chamber is used to lubricate the screw rotor sliding on the casing, and to seal between the screw rotor and the casing to ensure gastightness of the fluid chambers. The lubricant oil supplied to the fluid chamber is used to cool the fluid compressed in the fluid chamber, or the screw rotor.
Temperature of the fluid compressed in the fluid chamber, and temperature of the screw rotor increase with increase in operating capacity of the screw compressor. Thus, the amount of the lubricant oil required to reduce the temperature increase of the fluid in the fluid chamber and the screw rotor increases with the increase in operating capacity of the screw compressor.
In the conventional screw compressor described above, the lubricant oil in the sump is supplied to the fluid chamber due to the difference in pressure between the sump and the fluid chamber. Specifically, when the difference in pressure between the sump and the fluid chamber is constant, a flow rate of the lubricant oil supplied from the sump to the fluid chamber is substantially kept constant even when the operating capacity of the screw compressor is changed. Thus, even when the operating capacity of the screw compressor is low, the flow rate of the lubricant oil supplied to the fluid chamber is kept as high as the flow rate required in accordance with the high operating capacity.
When the screw compressor is operated, the screw rotor is rotated while stirring the lubricant oil supplied to the fluid chamber. The lubricant oil is viscous to a certain extent. Thus, the screw rotor is rotated against the viscosity of the lubricant oil. Specifically, power transmitted from a power source such as an electric motor etc. to the screw rotor is used not only to compress the fluid in the fluid chamber, but also to rotate the screw rotor against the viscosity of the lubricant oil. Thus, the flow rate of the lubricant oil supplied to the fluid chamber is preferably as low as possible at which the screw rotor is reliably lubricated and cooled.
In the conventional screw compressor in which the lubricant oil in the sump is supplied to the fluid chamber due to the difference in pressure between the sump and the fluid chamber, the flow rate of the lubricant oil supplied to the fluid chamber is substantially constant irrespective of the operating capacity of the screw compressor. Thus, when the operating capacity of the screw compressor is low, the flow rate of the lubricant oil supplied to the fluid chamber is too high, and greater power is required to rotate the screw rotor against the viscosity of the lubricant oil. This disadvantageously reduces efficiency of operation of the screw compressor.
In view of the foregoing, the present invention has been achieved. An object of the present invention is to improve the efficiency of operation of the screw compressor by reducing power required to rotate the screw rotor when the operating capacity of the screw compressor is low.
A first aspect of the invention is directed to a screw compressor including: a casing (10); and a screw rotor (40) which is inserted in a cylinder portion (30, 35) of the casing (10) to form a fluid chamber (23), the screw rotor (40) rotating to suck a fluid into the fluid chamber (23) for compression. The screw compressor includes an oil sump (17) which contains lubricant oil, a lubrication passage (110) which supplies the lubricant oil in the oil sump (17) to the fluid chamber (23) due to a difference in pressure between the oil sump (17) and the fluid chamber (23), and a flow rate controller (100) which reduces a flow rate of the lubricant oil supplied to the fluid chamber (23) in accordance with decrease in operating capacity of the screw compressor.
In the first aspect of the invention, the screw rotor (40) is contained in the casing (10). When the screw rotor (40) is rotated by an electric motor etc., the fluid is sucked into the fluid chamber (23), and is compressed. The lubricant oil in the oil sump (17) is supplied to the fluid chamber (23) formed by the screw rotor (40) through the lubrication passage (110). When the screw compressor (1) is operated, the screw rotor (40) is rotated while stirring the lubricant oil supplied to the fluid chamber (23). The flow rate controller (100) adjusts the flow rate of the lubricant oil supplied from the oil sump (17) to the fluid chamber (23) through the lubrication passage (110) in accordance with the operating capacity of the screw compressor (1). Specifically, the flow rate controller (100) reduces the flow rate of the lubricant oil supplied to the fluid chamber (23) as the operating capacity of the screw compressor (1) decreases. The flow rate controller (100) may change the flow rate of the lubricant oil supplied to the fluid chamber (23) in a continuous or stepwise manner.
According to a second aspect of the invention related to the first aspect of the invention, the screw compressor further includes: low pressure space (S1) which is formed in the casing (10), and into which uncompressed, low pressure fluid flows; a bypass passage (33) which is opened in an inner peripheral surface of the cylinder portion (30, 35) to communicate the fluid chamber (23) which finished a suction phase with the low pressure space (S1); and a slide valve (70) which slides in an axial direction of the screw rotor (40) to change an opening area of the bypass passage (33) in the inner peripheral surface of the cylinder portion (30, 35), wherein the lubrication passage (110) includes a stationary oil passage (120) having an outlet end (121) which is opened in a sliding surface (37) of the cylinder portion (30, 35) sliding on the slide valve (70), and a movable oil passage (130) having an inlet end (131) which is opened in a sliding surface (76) of the slide valve (70) sliding on the cylinder portion (30, 35), and an outlet end (132) which is opened in a sliding surface (72) of the slide valve (70) sliding on the screw rotor (40), the stationary oil passage (120) and the movable oil passage (130) are configured in such a manner that an area of the inlet end (131) of the movable oil passage (130) overlapping with the outlet end (121) of the stationary oil passage (120) is reduced as the slide valve (70) is moved to increase the opening area of the bypass passage (33), and the stationary oil passage (120) and the movable oil passage (130) constitute the flow rate controller (100).
In the second aspect of the invention, the screw compressor (1) includes the slide valve (70). When the slide valve (70) is moved, the opening area of the bypass passage (33) opened in the inner peripheral surface of the cylinder portion (30, 35) is changed. The change in opening area of the bypass passage (33) changes the operating capacity of the screw compressor (1). Specifically, when the slide valve (70) is moved to increase the opening area of the bypass passage (33), the flow rate of the fluid returning from the fluid chamber (23) to the low pressure space (S1) through the bypass passage (33) is increased, and the operating capacity of the screw compressor (1) is reduced. Conversely, when the slide valve (70) is moved to reduce the opening area of the bypass passage (33), the flow rate of the fluid returning from the fluid chamber (23) to the low pressure space (S1) through the bypass passage (33) is reduced, and the operating capacity of the screw compressor (1) is increased.
In the second aspect of the invention, the stationary oil passage (120) is formed the cylinder portion (30, 35), and the movable oil passage (130) is formed in the slide valve (70). The lubricant oil flowing from the oil sump (17) to the fluid chamber (23) passes through the outlet end (121) of the stationary oil passage (120) and the inlet end (131) of the movable oil passage (130), and is supplied to the fluid chamber (23) through the outlet end (132) of the movable oil passage (130). In the present invention, the area of the inlet end (131) of the movable oil passage (130) overlapping with the outlet end (121) of the stationary oil passage (120) is reduced as the slide valve (70) is moved to increase the opening area of the bypass passage (33). Thus, when the opening area of the bypass passage (33) is increased, and the operating capacity of the screw compressor (1) is reduced, the flow rate of the lubricant oil flowing from the stationary oil passage (120) to the movable oil passage (130) is reduced, and the flow rate of the lubricant oil supplied from the movable oil passage (130) to the fluid chamber (23) is reduced.
According to a third aspect of the invention related to the second aspect of the invention, the inlet end (131) of the movable oil passage (130) is divided into a plurality of branch passages (133, 134), and the branch passages (133, 134) of the movable oil passage (130) are opened in the sliding surface (76) of the cylinder portion (30, 35) sliding on the slide valve (70) in such a manner that the number of the branch passages (133, 134) communicating with the stationary oil passage (120) is reduced as the slide valve (70) is moved to increase the opening area of the bypass passage (33).
In the third aspect of the invention, the branch passages (133, 134) of the movable oil passage (130) are opened in the sliding surface (76) of the slide valve (70) sliding on the cylinder portion (30, 35). The number of the branch passages (133, 134) of the movable oil passage (130) communicating with the stationary oil passage (120) is reduced as the slide valve (70) is moved to increase the opening area of the bypass passage (33). Specifically, when the slide valve (70) is moved to increase the opening area of the bypass passage (33), the area of the inlet end (131) of the movable oil passage (130) overlapping with the outlet end (121) of the stationary oil passage (120) is reduced.
According to a fourth aspect of the invention related to the first aspect of the invention, the screw compressor further includes: an opening-variable flow rate control valve (111) which adjusts the flow rate of the lubricant oil flowing through the lubrication passage (110); and an opening controller (142) which reduces the degree of opening of the flow rate control valve (111) in accordance with decrease in operating capacity of the screw compressor, wherein the flow rate control valve (111) and the opening controller (142) constitute the flow rate controller (100).
In the fourth aspect of the invention, when the degree of opening of the flow rate control valve (111) is changed, the flow rate of the lubricant oil flowing through the lubrication passage (110) is changed, and the flow rate of the lubricant oil supplied to the fluid chamber (23) through the lubrication passage (110) is changed. When the operating capacity of the screw compressor (1) is reduced, opening controller (142) reduces the degree of the opening of the flow rate control valve (111). Thus, when the operating capacity of the screw compressor (1) is reduced, the flow rate of the lubricant oil supplied to the fluid chamber (23) through the lubrication passage (110) is reduced.
According to a fifth aspect of the invention related to the fourth aspect of the invention, the screw compressor further includes: a rotational speed-variable electric motor (15) for driving the screw rotor (40), wherein the opening controller (142) is configured to reduce the degree of opening of the flow rate control valve (111) in accordance with decrease in rotational speed of the electric motor (15).
In the fifth aspect of the invention, the screw rotor (40) is driven by the electric motor (15). When the rotational speed of the electric motor (15) is changed, the rotational speed of the screw rotor (40) is changed, and the operating capacity of the screw compressor (1) is changed. The operating capacity of the screw compressor (1) decreases with decrease rotational speed of the screw. Thus, the opening controller (142) adjusts the degree of opening of the flow rate control valve (111) in accordance with the rotational speed of the electric motor (15). Specifically, when the rotational speed of the electric motor (15) is reduced, the opening controller (142) reduces the degree of opening of the flow rate control valve (111). Therefore, the flow rate of the lubricant oil supplied to the fluid chamber (23) through the lubrication passage (110) is reduced.
According to a sixth aspect of the invention related to the fourth aspect of the invention, the screw compressor further includes: low pressure space (S1) which is formed in the casing (10), and into which uncompressed, low pressure fluid flows; a bypass passage (33) which is opened in an inner peripheral surface of the cylinder portion (30, 35) to communicate the fluid chamber (23) which finished a suction phase with the low pressure space (S1); and a slide valve (70) which slides in an axial direction of the screw rotor (40) to change an opening area of the bypass passage (33) in the inner peripheral surface of the cylinder portion (30, 35), wherein the opening controller (142) is configured to reduce the degree of opening of the flow rate control valve (111) as the slide valve (70) is moved to increase the opening area of the bypass passage (33).
In the sixth aspect of the invention, the screw compressor (1) includes the slide valve (70). As described in connection with the second aspect of the invention, the operating capacity of the screw compressor (1) is changed when the slide valve (70) is moved. Specifically, the operating capacity of the screw compressor (1) is reduced when the slide valve (70) is moved to increase the opening area of the bypass passage (33). The operating capacity of the screw compressor (1) is increased when the slide valve (70) is moved to reduce the opening area of the bypass passage (33).
In the sixth aspect of the invention, the operating capacity of the screw compressor (1) is changed when the slide valve (70) is moved. Thus, the opening controller (142) adjusts the degree of opening of the flow rate control valve (111) in accordance with the position of the slide valve (70). Specifically, the opening controller (142) reduces the degree of opening of the flow rate control valve (111) when the slide valve (70) is moved to increase the opening area of the bypass passage (33). Thus, the flow rate of the lubricant oil supplied to the fluid chamber (23) through the lubrication passage (110) is reduced.
According to a seventh aspect of the invention related to any one of the fourth to sixth aspect of the invention, the flow rate control valve (111) and the opening controller (142) are attached to the casing (10).
In the seventh aspect of the invention, the flow rate control valve (111) and the opening controller (142) are attached to the casing (10). The opening controller (142) adjusts the flow rate of the lubricant oil flowing through the lubrication passage (110) by adjusting the degree of opening of the flow rate control valve (111).
In the screw compressor (1) of the present invention, the lubricant oil is supplied to the fluid chamber (23) due to the difference in pressure between the oil sump (17) and the fluid chamber (23). Thus, unless special measures are taken, the flow rate of the lubricant oil supplied to the fluid chamber (23) is kept constant as long as the difference in pressure between the oil sump (17) and the fluid chamber (23) is constant even when the operating capacity of the screw compressor (1) is changed.
According to the present invention, the screw compressor (1) includes the flow rate controller (100). The flow rate controller (100) reduces the flow rate of the lubricant oil supplied to the fluid chamber (23) when the operating capacity of the screw compressor (1) is reduced.
Specifically, in the screw compressor (1) of the present invention, the flow rate controller (100) reduces the flow rate of the lubricant oil supplied to the fluid chamber (23) when the operating capacity of the screw compressor is reduced and supply of a large amount of the lubricant oil to the fluid chamber (23) is no longer necessary. When the amount of the lubricant oil supplied to the fluid chamber (23) is reduced, power required to rotate the screw rotor (40) against the viscosity of the lubricant oil is reduced.
Thus, according to the present invention, the power required to drive the screw rotor (40) can sufficiently be reduced when the operating capacity of the screw compressor (1) is reduced, and efficiency of operation of the screw compressor (1) can be kept high irrespective of the operating capacity of the screw compressor (1).
In the second and third aspects of the present invention, the area of the inlet end (131) of the movable oil passage (130) overlapping with the outlet end (121) of the stationary oil passage (120) is changed when the slide valve (70) is moved to change the operating capacity of the screw compressor (1). Thus, the flow rate of the lubricant oil flowing from the stationary oil passage (120) to the movable oil passage (130) is reduced, and the flow rate of the lubricant oil supplied from the movable oil passage (130) to the fluid chamber (23) is changed.
According to the second and third aspects of the invention, the flow rate of the lubricant oil supplied from the movable oil passage (130) to the fluid chamber (23) can be changed by using the slide valve (70) which is moved to change the operating capacity of the screw compressor (1). Thus, according to these aspects, the flow rate of the lubricant oil supplied to the fluid chamber (23) can reliably be changed in accordance with the operating capacity of the screw compressor (1) without providing additional sensors and controllers.
According to the fourth, fifth, and sixth aspects of the invention, the opening controller (142) adjusts the degree of opening of the flow rate control valve (111) in accordance with the operating capacity of the screw compressor (1). Thus, according to these aspects, the flow rate of the lubricant oil supplied to the fluid chamber (23) can reliably be set in accordance with the operating capacity of the screw compressor (1).
According to the seventh aspect of the invention, the flow rate control valve (111) is attached to the casing (10). Thus, as compared with the case where the flow rate control valve (111) is arranged away from the casing (10), the lubrication passage (110) can be shortened. Thus, the change in flow rate of the lubricant oil can be more responsive to the change in degree of opening of the flow rate control valve (111), and the flow rate of the lubricant oil supplied to the fluid chamber (23) can precisely be adjusted.
According to the seventh aspect of the invention, both of the flow rate control valve (111) and the opening controller (142) are attached to the casing (10). Thus, connecting the flow rate control valve (111) and the opening controller (142) through wires etc. can be performed in assembling the screw compressor (1) (i.e., before shipping of the screw compressor (1) from the factory). Therefore, in setting the screw compressor (1), the connection of the flow rate control valve (111) and the opening controller (142) is no longer necessary, thereby facilitating the setting of the screw compressor (1).
Embodiments of the present invention will be described in detail below with reference to the drawings.
A single screw compressor (1) of the present embodiment (hereinafter merely referred to as a screw compressor) is provided in a refrigerant circuit for performing a refrigeration cycle, and compresses a refrigerant.
As shown in
The casing (10) is in the shape of a horizontally-oriented cylinder. Space inside the casing (10) is divided into low pressure space (S1) close to an end of the casing (10), and high pressure space (S2) close to the other end of the casing (10). A suction pipe connector (11) communicating with the low pressure space (S1), and a discharge pipe connector (12) communicating with the high pressure space (S2) are formed in the casing (10). A low pressure gaseous refrigerant (i.e., low pressure fluid) flowed from an evaporator of the refrigerant circuit passes through the suction pipe connector (11) to enter the low pressure space (S1). A compressed, high pressure gaseous refrigerant discharged from the compression mechanism (20) to the high pressure space (S2) passes through the discharge pipe connector (12), and is supplied to a condenser of the refrigerant circuit.
In the casing (10), the electric motor (15) is arranged in the low pressure space (S1), and the compression mechanism (20) is arranged between the low pressure space (S1) and the high pressure space (S2). A drive shaft (21) of the compression mechanism (20) is coupled to the electric motor (15). A commercial power supply (201) is connected to the electric motor (15) of the screw compressor (1). The electric motor (15) rotates at constant rotational speed when alternating current is supplied from the commercial power supply (201).
An oil separator (16) is arranged in the high pressure space (S2) in the casing (10). The oil separator (16) separates refrigeration oil from the refrigerant discharged from the compression mechanism (20). An oil sump (17) for containing the refrigeration oil as lubricant oil is provided in the high pressure space (S2) below the oil separator (16). The refrigeration oil separated from the refrigerant by the oil separator (16) flows downward, and is contained in the oil sump (17).
As shown in
A bearing holder (35) is inserted in an end of the cylindrical wall (30) closer to the high pressure space (S2). The bearing holder (35) is in the shape of a slightly thick cylinder. An outer diameter of the bearing holder (35) is substantially the same as a diameter of an inner peripheral surface of the cylindrical wall (30) (i.e., a surface which slides on an outer peripheral surface of the screw rotor (40)). Part of an outer peripheral surface of the bearing holder (35) which slides on a slide valve (70) described later constitutes a guide surface (37) which is a sliding surface. Ball bearings (36) are provided in the bearing holder (35). A tip end of the drive shaft (21) is inserted in the ball bearings (36), and the ball bearings (36) rotatably support the drive shaft (21).
As shown in
Each of the helical grooves (41) of the screw rotor (40) has a front end in
Each of the gate rotors (50) is a resin member. Each of the gate rotors (50) includes a plurality of radially arranged, rectangular plate-shaped gates (51) (11 gates in this embodiment). Each of the gate rotors (50) is arranged outside the cylindrical wall (30) to be axially symmetric with the axis of rotation of the screw rotor (40). An axial center of each of the gate rotors (50) is perpendicular to an axial center of the screw rotor (40). Each of the gate rotors (50) is arranged in such a manner that the gates (51) penetrate part of the cylindrical wall (30) to mesh with the helical grooves (41) of the screw rotor (40).
The gate rotors (50) are attached to metal rotor supports (55), respectively (see
Each of the rotor supports (55) to which the gate rotor (50) is attached is placed in a gate rotor chamber (90) which is provided adjacent to the cylindrical wall (30) in the casing (10) (see
In the compression mechanism (20), space surrounded by the inner peripheral surface of the cylindrical wall (30), the helical groove (41) of the screw rotor (40), and the gate (51) of the gate rotor (50) constitutes a fluid chamber (23). An end of the helical groove (41) of the screw rotor (40) through which the refrigerant is sucked is opened toward the low pressure space (S1), and the open end constitutes an inlet (24) of the compression mechanism (20).
The screw compressor (1) includes a slide valve (70) for controlling capacity. The slide valve (70) is placed in a slide valve container (31). The slide valve container (31) is formed with two parts of the cylindrical wall (30) expanded radially outward, and each of the two parts is substantially in the shape of a semi-cylinder extending from a discharge end (a right end in
Communication passages (32) are formed in the casing (10) outside the cylindrical wall (30). The communication passages (32) are provided to correspond to the two parts of the slide valve container (31), respectively. The communication passage (32) is a passage extending in the axial direction of the cylindrical wall (30), and has an end opened in the low pressure space (S1) and the other end opened in the suction end of the slide valve container (31). Part of the cylindrical wall (30) adjacent to the other end of the communication passage (32) (a right end in
When the slide valve (70) slides closer to the high pressure space (S2) (to the right provided that the axial direction of the drive shaft (21) shown in
The screw compressor (1) includes a slide valve driving mechanism (80) for sliding the slide valve (70). The slide valve driving mechanism (80) includes a cylinder (81) fixed to the bearing holder (35), a piston (82) inserted in the cylinder (81), an arm (84) coupled to a piston rod (83) of the piston (82), a coupling rod (85) which couples the arm (84) and the slide valve (70), and a spring (86) which biases the arm (84) to the right in
In the slide valve driving mechanism (80) shown in
When the screw compressor (1) is being operated, suction pressure of the compression mechanism (20) is acted on one of axial end faces of the slide valve (70), and discharge pressure of the compression mechanism (20) is acted on the other axial end face. Thus, during the operation of the screw compressor (1), the slide valve (70) always receives force which presses the slide valve (70) toward the low pressure space (S1). When the inner pressures in the spaces on the left and right of the piston (82) in the slide valve driving mechanism (80) are changed, force which pulls the slide valve (70) back to the high pressure space (S2) is changed, thereby changing the position of the slide valve (70).
The slide valve (70) will be described in detail with reference to
The slide valve (70) includes a valve portion (71), a guide portion (75), and a coupling portion (77). The valve portion (71), the guide portion (75), and the coupling portion (77) of the slide valve (70) are formed with a single metal member. Specifically, the valve portion (71), the guide portion (75), and the coupling portion (77) are integrated.
The valve portion (71) is in the shape of a solid column which is partially cut away as shown in
An end face of the valve portion (71) (a left end face in
The guide portion (75) is in the shape of a column having a T-shaped cross-section. A side surface of the guide portion (75) corresponding to an arm of the T-shaped cross-section (i.e., a front side surface in
The coupling portion (77) is in the shape of a relatively short column, and couples the valve portion (71) and the guide portion (75). The coupling portion (77) is positioned opposite the sliding surface (72) of the valve portion (71) and the sliding surface (76) of the guide portion (75). Space between the valve portion (71) and the guide portion (75) of the slide valve (70) and space behind the guide portion (75) (space opposite the sliding surface (76)) form a passage for discharged gaseous refrigerant, and space between the sliding surface (72) of the valve portion (71) and the sliding surface (76) of the guide portion (75) is the outlet (25).
The screw compressor (1) includes a lubrication passage (110) through which the refrigeration oil contained in the oil sump (17) to the compression mechanism (20).
As shown in
As shown in
An inlet end (131) of the movable oil passage (130) is divided into a first branch passage (133) and a second branch passage (134). As shown in
An outlet end (132) of the movable oil passage (130) is formed in the sliding surface (72) of the valve portion (71). Specifically, the outlet end (132) of the movable oil passage (130) faces the outer peripheral surface of the screw rotor (40). The refrigeration oil discharged out of the outlet end (132) flows into the fluid chamber (23) formed by the helical groove (41) of the screw rotor (40).
The position of the inlet end (131) of the movable oil passage (130) in the sliding surface (76) of the slide valve (70) will be described in detail with reference to
In the state shown in
In the screw compressor (1) of the present embodiment, the movable oil passage (130) including the first and second branch passages (133, 134), and the stationary oil passage (120) including the outlet end (121) formed with the recess (122) constitute a flow rate controller (100) which adjusts the flow rate of the refrigeration oil supplied to the fluid chamber (23) in accordance with operating capacity of the screw compressor (1).
A working mechanism of the screw compressor (1) will be described with reference to
When the electric motor (15) of the screw compressor (1) is driven, the drive shaft (21) is rotated to rotate the screw rotor (40). As the screw rotor (40) is rotated, the gate rotors (50) are also rotated, and a suction phase, a compression phase, and a discharge phase of the compression mechanism (20) are repeated. In the following description, the fluid chamber (23) which is shaded in
In
When the screw rotor (40) is further rotated, the fluid chamber (23) is in the state shown in
When the screw rotor (40) is further rotated, the fluid chamber (23) is in the state shown in
Adjustment of capacity of the compression mechanism (20) using the slide valve (70) will be described with reference to
When the slide valve (70) is pushed to the leftmost position in
When the slide valve (70) moves to the right in
When the distance between the end face (P2) of the slide valve (70) and the seat surface (P1) of the slide valve container (31) is increased (i.e., an opening area of the bypass passage (33) in the inner peripheral surface of the cylindrical wall (30) is increased), the amount of the refrigerant returning to the low pressure space (S1) through the bypass passage (33) is increased, and the amount of the refrigerant discharged to the high pressure space (S2) is reduced. Specifically, the capacity of the compression mechanism (20) is reduced with the increase in distance between the end face (P2) of the slide valve (70) and the seat surface (P1) of the slide valve container (31).
The refrigerant discharged from the fluid chamber (23) to the high pressure space (S2) first flows into the outlet (25) formed in the slide valve (70). Then, the refrigerant flows into the high pressure space (S2) through the passage formed behind the guide portion (75) of the passage slide valve (70).
First, operation of supplying the refrigeration oil in the oil sump (17) to the compression mechanism (20) will be described below.
As described above, the lubrication passage (110) formed in the screw compressor (1) includes the stationary oil passage (120) and the movable oil passage (130), and the stationary oil passage (120) and the movable oil passage (130) communicate with each other. The oil sump (17) to which the lubrication passage (110) is connected is formed in the high pressure space (S2) in the casing (10), and pressure of the refrigeration oil contained in the oil sump (17) is substantially the same as the pressure of the high pressure gaseous refrigerant discharged from the compression mechanism (20). The outlet end (132) of the movable oil passage (130) is opened in the sliding surface (72) of the slide valve (70), and can communicate with the fluid chamber (23) in the suction phase. The low pressure gaseous refrigerant flows from the low pressure space (S1) to the fluid chamber (23) in the suction phase. Specifically, the inner pressure of the fluid chamber (23) in the suction phase is substantially the same as the pressure of the low pressure gaseous refrigerant in the low pressure space (S1).
Thus, the oil sump (17) connected to the lubrication passage (110) and the fluid chamber (23) have a difference in pressure. Thus, the high pressure refrigeration oil in the oil sump (17) flows through the lubrication passage (110), and is supplied to the fluid chamber (23). Specifically, in the screw compressor (1) of the present embodiment, the refrigeration oil in the oil sump (17) is supplied to the fluid chamber (23) due to the difference in pressure between the oil sump (17) and the fluid chamber (23). The refrigeration oil supplied to the fluid chamber (23) is supplied to sliding parts of the compression mechanism (20) (e.g., part of the screw rotor (40) sliding on the cylindrical wall (30)), thereby lubricating the sliding parts. Part of the refrigeration oil which entered the fluid chamber (23) enters a gap between the screw rotor (40) and the cylindrical wall (30) to form an oil film, thereby sealing the adjacent helical grooves (41).
Operation of adjusting the flow rate of the refrigeration oil supplied to the fluid chamber (23) will be described with reference to
In the state shown in
In the state shown in
In the state shown in
In the state shown in
When the distance between the end face (P2) of the slide valve (70) and the seat surface (P1) of the cylindrical wall (30) is smaller than a predetermined value, both of the first branch passage (133) and the second branch passage (134) of the movable oil passage (130) are opened in the stationary oil passage (120). When the distance between the end face (P2) of the slide valve (70) and the seat surface (P1) of the cylindrical wall (30) is the predetermined value or larger, only the first branch passage (133) of the movable oil passage (130) is opened in the stationary oil passage (120). Thus, the flow rate of the refrigeration oil supplied from the movable oil passage (130) to the fluid chamber (23) varies in a stepwise manner (in two steps in this embodiment) in accordance with change in operating capacity of the screw compressor (1).
In the screw compressor (1) of the present embodiment, the refrigeration oil is supplied to the fluid chamber (23) due to the difference in pressure between the oil sump (17) and the fluid chamber (23). Thus, unless special measures are taken, the flow rate of the refrigeration oil supplied to the fluid chamber (23) is kept constant as long as the difference in pressure between the oil sump (17) and the fluid chamber (23) is constant even when the operating capacity of the screw compressor (1) is changed.
In the screw compressor (1) of the present embodiment, the stationary oil passage (120) is formed in the bearing holder (35), the movable oil passage (130) is formed in the slide valve (70), and the area of the inlet end (131) of the movable oil passage (130) overlapping with the outlet end (121) of the stationary oil passage (120) varies depending on the position of the slide valve (70). In this screw compressor (1), the flow rate of the refrigeration oil supplied to the fluid chamber (23) through the stationary oil passage (120) and the movable oil passage (130) is reduced in accordance with the decrease in operating capacity of the screw compressor (1).
Specifically, in the screw compressor (1) of the present embodiment, the flow rate of the refrigeration oil actually supplied to the fluid chamber (23) is reduced when the operating capacity of the screw compressor is reduced, and a large amount of the refrigeration oil to the fluid chamber (23) is no longer necessary. When the amount of the refrigeration oil supplied to the fluid chamber (23) is reduced, power required to rotate the screw rotor (40) against the viscosity of the refrigeration oil is reduced, thereby reducing power consumed by the electric motor (15). Thus, the present embodiment can sufficiently reduce the power required to drive the screw rotor (40) when the operating capacity of the screw compressor (1) is reduced, and efficiency of operation of the screw compressor (1) can be kept high irrespective of the operating capacity of the screw compressor (1).
As described above, in the screw compressor (1) of the present embodiment, the area of the inlet end (131) of the movable oil passage (130) overlapping with the outlet end (121) of the stationary oil passage (120) is changed when the slide valve (70) is moved to change the operating capacity of the screw compressor (1), and the flow rate of the refrigeration oil supplied from the movable oil passage (130) to the fluid chamber (23) is changed. Thus, according to the present embodiment, the flow rate of the refrigeration oil supplied from the movable oil passage (130) to the fluid chamber (23) can be changed by using the slide valve (70) which is moved to change the operating capacity of the screw compressor (1). Thus, the present embodiment can reliably change the flow rate of the refrigeration oil supplied to the fluid chamber (23) in accordance with the operating capacity of the screw compressor (1) without providing additional sensors or controllers.
As shown in
The position of the recess (135) formed in the sliding surface (76) of the slide valve (70) will be described. In the state shown in
In the state shown in
In the state shown in
In the screw compressor (1) of this alternative example, a length of the part of the recess (135) formed in the slide valve (70) overlapping with the recess (122) formed in the bearing holder (35) is continuously changed in accordance with the distance between the end face (P2) of the slide valve (70) and the seat surface (P1) of the cylindrical wall (30). Thus, the flow rate of the refrigeration oil supplied from the movable oil passage (130) to the fluid chamber (23) is continuously changed in accordance with the change in operating capacity of the screw compressor (1).
A second embodiment of the present invention will be described. The screw compressor (1) of the present embodiment is provided by adding an inverter (200), a controller (140), and a flow rate control valve (111) to the screw compressor (1) of the first embodiment. In the screw compressor (1) of the present embodiment, the shapes of the stationary oil passage (120) and the movable oil passage (130) are different from those of the first embodiment. The differences between the screw compressor (1) of the present embodiment and the screw compressor of the first embodiment will be described below.
As shown in
When the output frequency of the inverter (200) is changed, rotational speed of the electric motor (15) is changed, and rotational speed of the screw rotor (40) driven by the electric motor (15) is changed. The change in rotational speed of the screw rotor (40) changes a mass flow rate of the fluid which is sucked into the single screw compressor (1) and discharged after compression. Specifically, the change in rotational speed of the screw rotor (40) changes operating capacity of the single screw compressor (1).
As shown in
The controller (140) includes an operating capacity control unit (141), and an oil amount control unit (142).
The operating capacity control unit (141) is configured to adjust the rotational speed of the screw rotor (40) in accordance with a load of the screw compressor (1). Specifically, the operating capacity control unit (141) is configured to determine a command value of the output frequency of the inverter (200) in accordance with the load of the screw compressor (1), and to output the determined command value to the inverter (200).
For example, when the pressure of the low pressure refrigerant sucked into the low pressure space (S1) (i.e., the low pressure of the refrigeration cycle) is lower than the predetermined target value, the operating capacity control unit (141) determines that the operating capacity of the screw compressor (1) is too high, and reduces the command value of the output frequency of the inverter (200). When the output frequency of the inverter (200) is reduced, the rotational speed of the screw rotor (40) driven by the electric motor (15) is reduced, and the operating capacity of the screw compressor (1) is reduced.
For example, when the pressure of the low pressure refrigerant sucked into the low pressure space (S1) is higher than the predetermined target value, the operating capacity control unit (141) determines that the operating capacity of the screw compressor (1) is too low, and increases the command value of the output frequency of the inverter (200). When the output frequency of the inverter (200) is increased, the rotational speed of the screw rotor (40) driven by the electric motor (15) is increased, and the operating capacity of the screw compressor (1) is increased.
The oil amount control unit (142) is configured to adjust the flow rate of the refrigeration oil supplied to the fluid chamber (23) through the lubrication passage (110) in accordance with the operating capacity of the screw compressor (1). The oil amount control unit (142) constitutes an opening controller for adjusting the degree of opening of the flow rate control valve (111). The oil amount control unit (142) constitutes a flow rate controller (100) together with the flow rate control valve (111).
Specifically, the command value of the output frequency determined by the operating capacity control unit (141) is input to the oil amount control unit (142). The oil amount control unit (142) determines a command value of the degree of opening of the flow rate control valve (111) in accordance with the command value of the output frequency of the inverter (200), and adjusts the degree of opening of the flow rate control valve (111) to the command value. For example, when the command value of the output frequency of the inverter (200) is the highest, the oil amount control unit (142) sets the degree of opening of the flow rate control valve (111) to the highest degree. The oil amount control unit (142) reduces the degree of opening of the flow rate control valve (111) in a continuous or stepwise manner in accordance with the decrease in command value of the output frequency of the inverter (200). Thus, the flow rate of the refrigeration oil supplied to the fluid chamber (23) through the lubrication passage (110) is reduced in a continuous or stepwise manner in accordance with the decrease in operating capacity of the screw compressor (1).
The oil amount control unit (142) does not fully open the flow rate control valve (111) even when the command value of the output frequency of the inverter (200) is the lowest. Thus, the amount of the refrigeration oil supplied to the fluid chamber (23) can be ensured even when the operating capacity of the screw compressor (1) is set to a lower limit value.
As described above, in the screw compressor (1) of the present embodiment, the shapes of the stationary oil passage (120) and the movable oil passage (130) are different from those of the first embodiment.
Specifically, the recess (122) is not formed in the bearing holder (35) of the present embodiment. Thus, the shape of the outlet end (121) of the stationary oil passage (120) in the guide surface (37) of the bearing holder (35) is the same as the shape of part of the stationary oil passage (120) connected to the outlet end (121).
The slide valve (70) of the present embodiment includes a recess (135) formed in the sliding surface (76) of the guide portion (75). The movable oil passage (130) of the present embodiment is a single passage which is not branched, and the recess (135) constitutes the inlet end (131) thereof. The recess (135) is a relatively short groove extending in the sliding direction of the slide valve (70) (i.e., the axial direction of the screw rotor (40)). The whole part of the outlet end (121) of the stationary oil passage (120) is opened in the recess (135) irrespective of the position of the slide valve (70).
In the screw compressor (1) of the present embodiment, the slide valve (70) may be omitted. The operating capacity of the screw compressor (1) of this alternative is adjusted by merely changing the rotational speed of the screw rotor (40).
In the screw compressor (1) of this alternative, the stationary oil passage (120) is formed in the cylindrical wall (30). In the cylindrical wall (30) of this alternative, the outlet end of the stationary oil passage (120) is opened in the inner peripheral surface of the cylindrical wall (30) which slides on the outer peripheral surface of the screw rotor (40). The refrigeration oil flowing from the oil sump (17) to the stationary oil passage (120) is discharged from the outlet end of the stationary oil passage (120) to the fluid chamber (23).
A third embodiment of the present invention will be described below. The screw compressor (1) of the present embodiment is different from the screw compressor (1) of the second embodiment except that the inverter (200) is omitted, a displacement sensor (143) is added, and the structure of the controller (140) is changed. The differences between the screw compressor (1) of the present embodiment and the screw compressor of the second embodiment will be described below.
The displacement sensor (143) is arranged to abut the slide valve (70), or an arm (84) or a coupling rod (85) coupled to the slide valve (70). The displacement sensor (143) outputs signals corresponding to the position of the slide valve (70) etc. to which the sensor abuts to the controller (140).
An operating capacity control unit (141) is configured to adjust the position of the slide valve (70) in accordance with the load of the screw compressor (1). Specifically, the operating capacity control unit (141) moves the slide valve (70) toward the high pressure space (S2) when it is determined that the operating capacity of the screw compressor (1) is too high, or moves the slide valve (70) toward the low pressure space (S1) when it is determined that the operating capacity of the screw compressor (1) is too low.
An oil amount control unit (142) is configured to adjust the flow rate of the refrigeration oil supplied to the fluid chamber (23) through the lubrication passage (110) in accordance with the operating capacity of the screw compressor (1). The oil amount control unit (142) constitutes a flow rate controller (100) together with the flow rate control valve (111).
Specifically, a signal output from the displacement sensor (143) (i.e., a signal representing the position of the slide valve (70)) is input to the oil amount control unit (142). The oil amount control unit (142) determines a command value of the degree of opening of the flow rate control valve (111) based on the output signal from the displacement sensor (143), and controls the degree of opening of the flow rate control valve (111) to the command value. For example, when it is determined that the slide valve (70) is positioned closest to the low pressure space (S1) based on the output signal from the displacement sensor (143), the oil amount control unit (142) sets the degree of opening of the flow rate control valve (111) to the highest. The oil amount control unit (142) reduces the degree of opening of the flow rate control valve (111) in a continuous or stepwise manner as the slide valve (70) is moved to increase the distance between the end face (P2) and the seat surface (P1). Thus, the flow rate of the refrigeration oil supplied to the fluid chamber (23) through the lubrication passage (110) is reduced in a continuous or stepwise manner in accordance with the decrease in operating capacity of the screw compressor (1).
The oil amount control unit (142) does not fully open the flow rate control valve (111) even when it is determined that the slide valve (70) is positioned closest to the high pressure space (S2). Thus, the amount of the refrigeration oil supplied to the fluid chamber (23) can be ensured even when the operating capacity of the screw compressor (1) is adjusted to a lower limit value.
In the screw compressor (1) of the second or third embodiment, both of the controller (140) and the flow rate control valve (111) are preferably attached to the casing (10) as shown in
In the screw compressor (1) shown in
The casing (10) of the screw compressor (1) shown in
As described above, the flow rate control valve (111) is attached to the casing (10) in the screw compressor (1) shown in
In the screw compressor (1) shown in
In the screw compressor (1) shown in
In the screw compressor (1) of the second or third embodiment, the movable oil passage (130) may be omitted, and the stationary oil passage (120) may be formed in the cylindrical wall (30). Specifically, in this alternative, the movable oil passage (130) is not provided in the slide valve (70). In the cylindrical wall (30) of this alternative, the outlet end of the stationary oil passage (120) is opened in the inner peripheral surface of the cylindrical wall (30) which slides on the outer peripheral surface of the screw rotor (40). The refrigeration oil flowed from the oil sump (17) to the stationary oil passage (120) is discharged from the outlet end of the stationary oil passage (120) to the fluid chamber (23).
Third Alternative
In the screw compressor (1) of the above embodiments, the oil sump (17) may be arranged outside the casing (10). In this case, a hermetic container is provided near the casing (10), and space inside the container constitutes the oil sump (17).
In the above embodiments, the present invention has been applied to the single screw compressors. However, the present invention may be applied to twin screw compressors (so-called Lysholm compressors).
As described above, the present invention is useful for screw compressors.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-062503 | Mar 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/001849 | 3/15/2010 | WO | 00 | 9/14/2011 |
