JP2013002289A - Screw compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that, in a screw compressor, the conventional internal volume ratio varying mechanism and control make the control method complicated and the control device expensive because an optimal Vi value calculated from discharge pressure and inlet pressure is used for the adjustment of opening of a variable Vi valve and it causes a deviation from the actual optimal Vi value, and also, in order to reduce the deviation, it is configured to execute the control for feeding back a transition of changes in motor driving power to position control.SOLUTION: A screw compressor includes an internal volume ratio varying mechanism having a variable Vi valve 8 to make the internal volume ratio Vi variable. The variable Vi valve 8 has a hole 14 through which tooth groove internal pressure before and after the discharge start is taken out. Position control of the variable Vi valve 8 is performed by driving the internal volume ratio varying mechanism (a drive unit 10) in reference to the tooth groove internal pressure taken out through the hole 14.

Description

  The present invention relates to a screw compressor, and more particularly to a screw compressor provided with a variable internal volume ratio Vi valve that adjusts the timing of discharge start according to an operating pressure ratio.

  A conventional screw compressor is equipped with a variable Vi valve that adjusts the discharge start timing to make the internal volume ratio Vi variable, and the opening degree of the variable Vi valve is adjusted by the driving force from the drive mechanism according to the operating pressure ratio. There is something which was made to do (for example, refer to patent documents 1).

  As shown in FIGS. 7 and 8, the conventional variable Vi valve calculates an optimum Vi value from the discharge pressure HP and the suction pressure LP, obtains the current Vi value from the position detection means, and obtains the current Vi value and the optimum Vi value. It is controlled by a drive mechanism connected to the variable Vi valve so that the difference from the value becomes small. Further, the opening degree of the variable Vi valve is adjusted so that the motor driving power is minimized in order to approach the optimum Vi value during actual operation.

  Here, the internal volume ratio Vi in the screw compressor is a ratio between the tooth space space at the time of suction and the tooth space space just before the discharge as shown in Patent Document 2, for example. It represents the ratio between the volume when completed and the volume when the discharge port opens. And, when the Vi valve is a fixed type screw compressor, for example, if a low compression ratio operation is performed with a medium compression ratio screw compressor, before the discharge port is opened, the gas is overcompressed above the discharge pressure, and excess Doing compression work. Conversely, when the operation is performed at a high compression ratio, the discharge port is opened before the discharge pressure is reached, so that a state of undercompression in which a backflow of gas occurs is obtained. All of these cause power loss and reduce efficiency.

Japanese Patent No. 4147891 (FIGS. 1 and 2) JP-A-62-87687 (2nd page)

In view of this, a variable Vi type screw compressor has been proposed in the past. In such a variable Vi type screw compressor, the optimum Vi value calculated from the discharge pressure and the suction pressure is used to adjust the opening of the variable Vi valve. There is a problem that a deviation from the actual optimum Vi value occurs.
In addition, as a conventional method for reducing the deviation, there is disclosed control in which a change transition of motor drive power is fed back to position control. However, there is a problem that the control method is complicated and the control device is expensive.

The present invention has been made to solve the above-described problems, and by taking out the internal pressure in the tooth gap from the inner discharge side end of the variable Vi valve and using it for control, the operation pressure ratio can be changed, Even when the internal pressure of the tooth gap changes due to leakage or the like, the internal pressure of the tooth gap before and after the actual discharge start is detected, the variable Vi valve is moved so that the internal volume ratio with the discharge pressure is optimized, and the variable Vi valve is accurately detected. It is an object of the present invention to provide a highly efficient screw compressor with a simple mechanism.
In addition, the internal pressure of the tooth space taken out from the inner discharge side end of the variable Vi valve is guided to the cylinder chamber that houses the piston connected to the variable Vi valve, and the difference between the pressure in the tooth space before and after the start of discharge and the discharge pressure. Accordingly, an object of the present invention is to provide a highly efficient screw compressor with a simple and inexpensive mechanism without requiring a complicated control device by automatically moving the variable Vi valve to an optimal position.

The screw compressor according to the present invention is a screw compressor including an internal volume ratio variable mechanism including a variable Vi valve for making the internal volume ratio Vi variable.
The variable Vi valve has a hole for taking out the internal pressure of the tooth gap before and after the start of discharge,
The position of the variable Vi valve is controlled by driving the internal volume ratio variable mechanism with reference to the internal pressure of the tooth space taken out from the hole.

  According to the present invention, it is possible to control and drive the variable Vi valve by detecting the internal pressure of the tooth space before and after the start of discharge without requiring a special control device or control flow. The performance of the compressor can be improved.

It is a schematic block diagram of the screw compressor which concerns on Embodiment 1 of this invention. It is a front view of a variable Vi valve. It is a schematic diagram of the internal volume ratio variable mechanism which concerns on Embodiment 1 of this invention. It is a figure which shows the pv diagram and piston load in an undercompressed state. It is a figure which shows the p-v diagram and piston load in an overcompressed state. It is a schematic block diagram of the screw compressor which concerns on Embodiment 2 of this invention. It is a schematic block diagram of the variable Vi type screw compressor of a prior art. It is a figure which shows the control system of the variable Vi type screw compressor of a prior art.

Embodiment 1 FIG.
FIG. 1 is a schematic configuration diagram of a screw compressor according to Embodiment 1 of the present invention.
The screw compressor according to the first embodiment is a single screw compressor, and as shown in FIG. 1, a cylindrical casing body 1 and a screw rotor 3 accommodated in the casing body 1. And a motor 2 that rotationally drives the screw rotor 3. The motor 2 includes a stator 2a that is inscribed and fixed to the casing body 1 and a motor rotor 2b that is disposed inside the stator 2a, and the rotational speed is controlled by an inverter system. The screw rotor 3 and the motor rotor 2 b are arranged on the same axis line, and both are fixed to the screw shaft 4. Further, the screw rotor 3 is formed with a plurality of spiral grooves (screw grooves), and is connected to a motor rotor 2 b fixed to the screw shaft 4 and is driven to rotate. The space of the adjacent groove formed on the cylindrical surface of the screw rotor 3 is surrounded by the inner cylinder surface of the casing body 1 and a pair of gate rotors (not shown) engaged with and engaged with the groove. Form. Further, the casing body 1 is separated from the discharge pressure side and the suction pressure side by a partition wall (not shown), and a pair of discharge ports 7 that open to the discharge chamber 6 are formed on the discharge pressure side. Further, the casing body 1 is provided with a pair of variable Vi valves 8 that are connected to a pair of rods 9 and a driving device 10 and are movable in the axial direction, and form a part of the discharge port 7. Note that the illustration of the drive device 10 connected to the other variable Vi valve 8 is omitted.

FIG. 2 is a front view of the variable Vi valve 8 as viewed from the inner surface side.
As shown in FIG. 2, the variable Vi valve 8 includes a valve body 8a, a guide portion 8b, and a connecting portion 8c, and a connecting portion 8c is provided at the inner surface discharge side end portion 8e of the guide portion 8b. The rod 9 is connected to the end face 8f on the driving device 10 side. Further, the valve body 8a and the guide portion 8b are connected by a connecting portion 8c, and a gap communicating with the discharge port 7 is formed. And the tooth | gear internal pressure taking-out hole 14 is provided in the vicinity of the inner surface discharge side edge part 8d of the valve main body 8a. Through this tooth gap pressure extraction hole 14, the tooth gap pressure of compressed gas before and after the start of discharge can be detected.

FIG. 3 is a schematic diagram of the internal volume ratio variable mechanism including the driving device 10.
The drive device 10 is a part of the internal volume ratio variable mechanism, and is configured to connect pistons 12 and 13 provided in the cylinder 11 and the variable Vi valve 8 with a rod 9.

As shown in FIG. 3, the driving device 10 is provided with a piston partition wall 15 that separates the space in the cylinder 11, and a first piston 12 and a second piston 13 are provided on both sides of the piston partition wall 15. The rod 9 connected to the variable Vi valve 8 passes through the first piston 12, the piston partition wall 15, and the second piston 13. Seal members 18 are attached to the cylinder fitting portions and the piston partition walls of the first piston 12 and the second piston 13.
Further, two first cylinder chambers 16a and 16b are formed on both sides of the first piston 12 on the front side (variable Vi valve direction) with respect to the piston partition wall 15, and the rear side (anti-variable Vi) with respect to the piston partition wall 15. Similarly, two second cylinder chambers 17a and 17b are formed on both sides of the second piston 13 in the valve direction. That is, the inside of the cylinder 11 is divided into four cylinder chambers 16a, 16b, 17a, and 17b in order from the front by the piston partition wall 15 and the two pistons 12 and 13.
The cylinder chambers 16a, 16b, 17a, and 17b include pressure introduction holes 116a, 116b, and 117a that are connected to the discharge chamber 6, the tooth gap internal pressure extraction hole 14, the discharge chamber 6, and the suction pressure chamber in the casing body 1, respectively. 117b.

Next, the communication path between the intradental pressure extraction hole 14 and the pressure introduction hole 116b will be described with reference to FIG.
The casing body 1 is provided with a communication passage 19 communicating with the tooth groove internal pressure extraction hole 14. The communication passage 19 and the tooth groove internal pressure extraction hole 14 are grooves extending in the axial direction on the surface (outer peripheral surface) of the variable Vi valve 8. Are communicated through a concave portion 20. In other words, the recess 20 is provided in such a range that the communication path 19 is always in the recess 20 even when the variable Vi valve 8 moves a predetermined distance, and the communication path 19 and the tooth pressure taking-out hole 14 are securely connected. It is comprised so that it may connect.
The communication passage 19 is provided by extending the inside of the wall of the casing body 1 in the direction of the cylinder 11 and is connected to the first cylinder chamber 16b.

Next, the operation of the variable Vi valve 8 will be described.
(I) Operation from the undercompressed state FIG. 4 is a diagram for explaining the operation from the undercompressed state. 4A is a pressure change in the compression chamber before the pressure balance, FIG. 4B is a pressure change in the compression chamber after the pressure balance, and FIG. 4C is a pressure distribution diagram in the variable Vi mechanism in the state of FIG. is there.

In the screw compressor, after the refrigerant gas is compressed and the pressure rises, the discharge port 7 is opened and discharged, but in the case of high compression ratio operation as shown in FIG. Even at the time of starting, the tooth gap internal pressure has not reached the discharge pressure, and is in an under-compressed state. In this way, in the undercompressed state, the tooth space pressure does not reach the discharge pressure even at the time when the discharge is started, so that a reverse flow of the refrigerant gas occurs, thereby causing a power loss.
Next, the pressure and operation acting on each piston and the variable Vi valve will be described with reference to FIG.
The suction pressure acts on the suction side end of the valve body 8a, and the pressure immediately after discharge acts on the end 8d. Further, the same pressure as that acting on the end portion 8d acts on the end portion 8e of the guide 8b, and the pressure of the discharge chamber 6 acts on the end portion 8f. That is, since the load acting on the end faces 8d and 8e inside the variable Vi valve is canceled, the load due to the differential pressure between the suction pressure and the discharge pressure acting on both ends acts on the variable Vi valve.
In the second cylinder chamber 17, the pressure of the discharge chamber 6 is introduced to the end face side where the rod 9 of the second piston 13 is connected, and the suction pressure is introduced to the opposite side. The direction of pressure acting on the second piston 13 acts in the opposite direction to that of the variable Vi valve, and the operating area also matches the presence or absence of the rod 9, so that the load acting on the variable Vi valve acts on the second piston. Is offset by the load

On the other hand, in the first cylinder chamber 16, the pressure of the discharge chamber 6 is introduced to the variable Vi side of the first piston 12, and the tooth gap takeout internal pressure is introduced to the opposite side. In the undercompressed state, the variable Vi valve 8 moves to the drive device 10 side (in the direction of the broken line arrow) due to the pressure difference between the discharge pressure and the pressure in the tooth gap before and after the start of discharge. That is, the variable Vi valve 8 moves in a direction in which the discharge start timing is delayed (in a direction in which the Vi value is increased), and reaches a state (optimum Vi value) in which the tooth gap pressure almost coincides with the discharge start pressure. The pressure change in the compression chamber changes from FIG. 4A with a large power loss to FIG. 4B with a small power loss, and the differential pressure with the first cylinder chamber 16 that drives the variable Vi valve is also small. Therefore, the operation is continued with a small power loss.
Note that the tooth gap internal pressure taken out from the tooth gap internal pressure takeout hole 14 at the inner discharge side end of the variable Vi valve 8 has a detection range as indicated by the white arrow in FIG. Adjustable by position.
From these things, the driving | operation with which the power loss by insufficient compression becomes small is attained, and the efficiency of a screw compressor can be improved.

(Ii) Operation from the overcompressed state FIG. 5 is a diagram for explaining the operation from the overcompressed state. In FIG. 5, (a) is the pressure change in the compression chamber before the variable Vi mechanism pressure balance, (b) is the pressure change in the compression chamber after the variable Vi mechanism pressure balance, and (c) is the variable Vi mechanism in (a). And the driving direction of the variable Vi mechanism.
In the case of the low compression ratio operation as shown in FIG. 5A, conversely, the pressure in the tooth gap has already exceeded the discharge pressure before starting the discharge of the refrigerant gas, and is in an overcompressed state. . Thus, in the overcompressed state, since the pressure in the tooth gap already exceeds the discharge pressure before the discharge is started, excessive compression work is performed, thereby causing a power loss. Further, the tooth gap internal pressure extracted from the tooth gap internal pressure extraction hole 14 at the inner surface discharge side end of the variable Vi valve 8 has a pressure detection range as shown in FIG. From this state, the relationship between the discharge pressure and the tooth gap internal pressure before and after the start of discharge is such that the discharge pressure is lower than the pressure gap before and after the discharge start, so that the first cylinder chamber has a variable Vi valve (right in FIG. 5 (c)). A load acts in the direction, and the piston and the variable Vi valve move in the direction of the variable Vi valve (right in FIG. 5C), that is, in the direction in which the internal volume ratio decreases. Since the variable Vi valve 8 moves in the direction of the variable Vi valve (right in FIG. 5C), that is, the direction in which the internal volume ratio decreases, the timing at which the discharge port opens becomes earlier, so the tooth gap before and after the start of discharge The extraction pressure decreases. At this time, as in the case of the undercompressed state, the load on the piston 13 provided in the second cylinder and the load acting on the variable Vi valve 8 are both the pressure difference between the discharge pressure and the suction pressure, and are therefore canceled out. ing. For these reasons, the variable Vi valve 8 moves to a position where the differential pressure between the tooth gap take-out pressure and the discharge pressure is small, that is, the optimum Vi value as shown in FIG. Therefore, an operation in which power loss due to overcompression is reduced is possible, and the efficiency of the screw compressor can be improved.

  As described above, according to the first embodiment, the second cylinder chamber and the second piston for canceling the load acting on the variable Vi valve by the pressure balance (having a function) and the tooth provided on the variable Vi valve are provided. Drive comprising the first cylinder chamber and the first piston having the function of automatically moving and adjusting the variable Vi valve 8 to the optimum position by utilizing the differential pressure between the tooth groove internal pressure from the groove internal pressure take-out hole and the discharge pressure. Since the mechanism is provided, a special apparatus is not required, and a highly efficient screw compressor can be obtained with a simple and inexpensive mechanism.

Embodiment 2. FIG.
FIG. 6 is a schematic configuration diagram of a screw compressor according to Embodiment 2 of the present invention.
In the first embodiment described above, the configuration in which one drive device 10 that automatically controls the axial movement of the variable Vi valve 8 by the differential pressure and balance of each pressure is provided for each valve. In the second embodiment, referring to the tooth gap internal pressure detected from the tooth gap internal pressure take-out hole 14 provided in the vicinity of the inner discharge side end of the variable Vi valve 8, the variable Vi valve is driven by the drive device 21 constituting the internal volume ratio variable mechanism. And an internal volume ratio control device 22 that controls the positions of the drive device 21 and the variable Vi valve 8.

  In the second embodiment, the variable Vi valve 8 is connected to the drive device 21 by the rod 9 and moves in the axial direction. This drive device 21 shows an example of an internal volume ratio variable mechanism. For example, a structure in which a piston 24 provided in a cylinder 23 and a rod 9 connected to a variable Vi valve 8 are connected by a connecting plate 25. It has become. Therefore, the variable Vi valve 8 is moved according to the movement of the piston 24 in the axial direction, and the discharge port 7 formed by the variable Vi valve 8 is moved to continuously change the internal volume ratio Vi. Can do.

  Further, the intradental pressure extracted from the intradental pressure extraction hole 14 is guided to the internal volume ratio controller 22 as shown in FIG. In other words, the internal volume ratio control device 22 detects the tooth gap internal pressure before and after the start of discharge through the tooth gap internal pressure extraction hole 14. The internal volume ratio control device 22 controls the fluid supply amount so that the detected tooth gap internal pressure becomes an optimum value corresponding to the operation condition (operation compression ratio), and the piston 24 of the drive device 21 is controlled. The variable Vi valve 8 is supplied to the front and rear cylinder chambers 26a and 26b and controlled to move to the optimum position in the axial direction.

  As described above, according to the second embodiment, the internal volume ratio control device 22 is referred to with reference to the tooth gap internal pressure extracted from the tooth gap internal pressure extraction hole 14 provided near the inner surface discharge side end of the variable Vi valve 8. By controlling the supply amount of the fluid supplied to the cylinder chamber 26 of the drive device 21 with, for example, the axial movement of the variable Vi valve 8, that is, the internal volume ratio is controlled, and the power loss is reduced with a simple structure. The performance of the screw compressor can be improved.

Embodiment 3 FIG.
In the first and second embodiments described above, since the pressure taken out from the hole near the inner surface discharge end of the variable Vi valve 8 is the pressure in the tooth space of the compressed gas, as shown in FIGS. Since there is a pressure change within the detection range, and a pressure change also occurs when straddling the tooth gap, a pressure pulsation occurs, and this pressure pulsation affects the drive of the variable Vi valve 8 due to a minute vibration or the like. May give. Therefore, it is necessary to reduce the propagation of this pressure pulsation to the internal volume ratio drive mechanism such as the pistons 12 and 13, and for this purpose, the path of the pressure extracted from the tooth space pressure extraction hole 14 of the variable Vi valve 8. A diaphragm mechanism (not shown) is provided inside. As a result, the pressure pulsation generated when detecting the pressure extracted from the tooth space pressure extraction hole 14 of the variable Vi valve 8 can be reduced, the internal volume ratio can be controlled with high accuracy, and the more stable screw compressor can be controlled. Performance can be improved.

  Further, the pistons 12, 13, and 24 connected to the variable Vi valve 8 may be one piston for two variable Vi valves as shown in FIG. 6, or the variable Vi valve as shown in FIG. One piston may be provided for one, and the number of pistons for the variable Vi valve 8 is not limited.

  Furthermore, by providing the sealing members 18 on the outer periphery and inner periphery of the pistons 12, 13, 24 and the piston partition wall 15, gas leakage between the cylinder chambers can be prevented, and the pressure in each cylinder chamber can be accurately maintained, The variable Vi valve 8 can be driven with high accuracy.

  Further, the internal volume ratio Vi may be adjusted by using the variable Vi valve 8 together with the gas bypass operation to the suction side.

  Further, the internal volume ratio variable mechanism may be a hydraulic cylinder or a motor having a position control function.

  In the first embodiment, a pair of tooth space pressure extraction holes 14 is provided, but may be provided in either one of the two variable Vi valves 8, which has an effect of reducing the processing cost.

  Further, capacity control for obtaining a desired operating pressure ratio can be realized by controlling the rotational speed of the motor 2 by inverter driving.

  1 casing body, 2 motor, 2a stator, 2b motor rotor, 3 screw rotor, 4 screw shaft, 5 compression chamber, 6 discharge chamber, 7 discharge port, 8 variable Vi valve, 8a valve body, 8b guide portion, 8c connecting portion 8d Inner surface discharge side end, 9 rod, 10 drive unit, 11 cylinder, 12 first piston, 13 second piston, 14 tooth space internal pressure extraction hole, 15 piston partition wall, 16, 16a, 16b first cylinder chamber, 17 , 17a, 17b Second cylinder chamber, 18 seal member, 19 communication passage, 20 recess, 21 drive device, 22 internal volume ratio control device, 23 cylinder, 24 piston, 25 connecting plate, 26, 26a, 26b cylinder chamber, 116a 116b, 117a, 117b Pressure introducing holes.

Claims (8)

In a screw compressor having an internal volume ratio variable mechanism including a variable Vi valve for making the internal volume ratio Vi variable,
The variable Vi valve has a hole for taking out the internal pressure of the tooth gap before and after the start of discharge,
A screw compressor that controls the position of the variable Vi valve by driving the internal volume ratio variable mechanism with reference to the internal pressure of the tooth space taken out from the hole.   The screw compressor according to claim 1, wherein the hole for taking out the tooth gap internal pressure is provided in the vicinity of an inner surface discharge side end portion of the variable Vi valve. The variable Vi valve is connected to the internal volume ratio variable mechanism via a rod,
The screw compressor according to claim 1 or 2, further comprising a control device that controls the internal volume ratio variable mechanism with reference to an internal pressure of the tooth space taken out from the hole. The internal volume ratio variable mechanism has a cylinder, a piston partition that separates the space in the cylinder, and two pistons provided on both sides of the piston partition,
A rod connected to the variable Vi valve is provided through the piston partition wall, the two pistons, and the cylinder,
The inside of the cylinder is divided into four space chambers by the piston partition wall and the two pistons,
The four space chambers are arranged as a discharge pressure chamber, a tooth space pressure chamber extracted from the hole, a discharge pressure chamber, and a suction pressure chamber in the order close to the variable Vi valve. 2. The screw compressor according to 2.   The screw compressor according to claim 4, wherein a throttling mechanism is provided in a path where the internal pressure of the tooth space taken out from the hole communicates with the internal volume ratio variable mechanism.   A communication passage communicating with the hole for taking out the tooth gap internal pressure is provided in the screw body, and the hole and the communication passage communicate with each other through a long recess in the axial direction provided on the outer peripheral surface of the variable Vi valve. The screw compressor according to any one of claims 1 to 5.   The screw compressor according to claim 1, wherein the internal volume ratio variable mechanism is configured by a hydraulic cylinder.   The screw compressor according to any one of claims 1 to 6, wherein the internal volume ratio variable mechanism is configured by a motor having a position control function.

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