JPH07259778A - Capacity control device for screw compressor - Google Patents

Abstract

PURPOSE:To ensure a proper control speed in a wide operation range where a differential pressure between high and low pressures is fluctuated and to provide a proper load up speed regardless of a cooling water temperature during starting. CONSTITUTION:When a differential pressure between high and low pressures is low during load up, only an on-off valve SV2 on the low resistance side is opened, and oil is discharged through a first discharge passage 8a on the load up side. When the level differential pressure is high, only an on-off valve SV3 on the high resistance side is opened and oil is discharged through a second discharge passage 8b on the load up side. This constitution improves drainage of oil from a chamber 51 on the load side when the differential pressure is low, prevents the occurrence of defective operation of load up and a delay of load up, and prevents a load up speed from being excessively increased when the differential pressure is high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacity control device for a screw compressor used in a refrigerator or the like.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Unexamined Patent Publication No. 2-248677, as shown in FIG. 7, a slide valve B is installed in a casing A which houses a screw rotor, and a front end surface of the slide valve B is installed in a low pressure region LP on the suction side. The rear end face is internally installed so as to face the high pressure region HP on the discharge side, the piston D is connected to the slide valve B via the rod C, and the piston D is provided in the cylinder chamber E provided on one side in the moving direction of the slide valve B. It is installed in.

In the rod side chamber F of the cylinder chamber E,
A high-pressure oil passage I communicating with an oil separator provided on the discharge side and having a check valve H, and a load-up discharge passage K having an opening / closing valve J and a throttle R opened at the time of load-up and communicating with a low pressure,
It is connected via a supply / discharge path L. Further, in the head side chamber G in the cylinder chamber E, an oil supply passage M branching from the primary side of the check valve H in the high pressure oil passage I, a load down discharge passage O having an opening / closing valve N and a throttle P opened during load down. And are connected.

Thus, on the basis of the cold water temperature of the evaporator in the refrigerator, the opening / closing valve J on the load-up side is opened and the opening / closing valve J on the load-down side is closed at the time of load-up, and conversely at the time of load-down. Open the on-off valve N on the down side,
The on-off valve J on the load-up side is closed, and by reversibly opening and closing these two on-off valves J and N, the slide valve B is moved by supplying and discharging high-pressure oil to the rod-side chamber F and increasing or decreasing pressure to the head-side chamber G. Capacity control by 2
Slide valve S by closing two on-off valves J and N together
Is held at an arbitrary position to generate cold water having a predetermined temperature.

[0005]

By the way, in the above, considering the state where the slide valve S is held at an arbitrary volume control position and the piston D is stationary, the rod side chamber F is considered.
The oil trapped inside acts on the sum of the urging force from the head-side chamber G and the urging force toward the load-up side based on the differential pressure acting on the front and rear end surfaces of the slide valve S. is doing. From this state, when the on-off valve J on the load-up side is opened and the slide valve S is moved to the load-up side, the oil trapped in the rod side chamber F will escape to the low pressure side via the throttle R, and the slide valve S moves to the load-up side at a speed according to the high and low differential pressure.

Therefore, if the conditions of high and low differential pressure change,
As shown in FIG. 8, the load-up time, that is, the time from the load-up start command until the load-up is actually completed changes, and the controllability when performing control to keep the cold water temperature constant is poor, There is a problem that the cold water temperature is easily disturbed. Especially, when the cooling water temperature on the condenser side is low, the high and low differential pressure is small and it is difficult to load up, and when the cooling water temperature is high, the high and low differential pressure is large. However, there is a problem that the load-up speed increases, the low pressure falls too low before the expansion valve is fully opened, and the low-pressure reduction safety device operates to cause an operation stop.

The main object of the present invention is a screw compression which can secure an appropriate control speed in a wide operating range in which the high and low differential pressure fluctuates, and can perform an appropriate load-up at the time of starting or the like regardless of the cooling water temperature and the like. The purpose is to provide a capacity control device for the machine.

[0008]

In order to achieve the above-mentioned main object, the invention according to claim 1 has a slide valve 3 disposed in a casing 1 for accommodating a screw rotor 2 as shown in FIG. A piston 4 connected to the slide valve 3 and a cylinder chamber 5 that houses the piston 4 are provided, and a supply / discharge passage 7 for supplying / discharging a discharge system high-pressure fluid is connected to the cylinder chamber 5, In a displacement control device of a screw compressor, which controls the displacement by moving a slide valve 3 connected to the piston 4 by supplying and discharging the high pressure fluid to and from a high pressure differential pressure between a suction side and a discharge side of the screw rotor 2. A valve control mechanism 80 for controlling the load-up speed of the slide valve 3 according to the change of

According to the second aspect of the present invention, since the valve control mechanism 80 is constructed at a low cost, the valve control mechanism 80 is provided with a plurality of load-up side discharge passages 8a having different flow resistances, as shown in FIG. 8b and on-off valves SV2 and SV that are respectively installed in the discharge passages 8a and 8b and open and close according to the high and low differential pressure.
It is composed of 3 and 3.

In order to enable the valve itself to automatically adjust the load-up speed in accordance with the fluctuation of the high and low differential pressure, the third aspect of the present invention, as shown in FIG. 2 and FIG. 3 or FIG. The valve control mechanism 80 is provided in the middle of the load-up side discharge passage 8, one end side communicates with the discharge side of the screw rotor 2 and the other end side communicates with the suction side of the screw rotor 2, and the suction side pressure A differential pressure valve having a valve body 84 that operates by a pressure difference from the discharge side pressure and adjusts the communication opening of the discharge passage 8 is adopted.

According to the fourth aspect of the present invention, since the control by the valve control mechanism 80 is finely performed, this valve control mechanism 80 is used.
As shown in FIG. 5, the electric valve is constituted by an electric valve MV interposed in the discharge passage 8 on the load-up side.

According to the fifth aspect of the present invention, in order to eliminate not only the load-up speed but also the change in the load-down speed due to the high and low differential pressure, as shown in FIG. Slide valve 3 to be installed,
A piston 4 connected to the slide valve 3 and a cylinder chamber 5 that houses the piston 4 are provided, and a supply / discharge passage 7 for supplying / discharging a discharge system high-pressure fluid is connected to the cylinder chamber 5 to connect to the cylinder chamber 5. In the displacement control device of the screw compressor, which controls the displacement by moving the slide valve 3 connected to the piston 4 by supplying and discharging the high-pressure fluid, the high-low differential pressure between the suction side and the discharge side of the screw rotor 2 A first valve control mechanism 80 for controlling the load-up speed of the slide valve 3 according to a change is provided, and the slide valve according to a change in height difference between the suction side and the discharge side of the screw rotor 2. The second valve control mechanism 90 for controlling the load-down speed of No. 3 is provided.

[0013]

According to the first aspect of the invention, the screw rotor 2
Since the load-up speed of the slide valve 3 is controlled according to the change in the height differential pressure between the suction side and the discharge side of, the proper load-up speed can be obtained, and when the height differential pressure is small,
It is possible to prevent a malfunction of the load-up and a delay in the load-up time from occurring, and also to prevent the load-up speed from becoming too fast when the high and low differential pressure is large.

According to the second aspect of the present invention, the load-up speed of the slide valve 3 can be set at a low cost by selectively opening and closing the on-off valves SV2 and SV3 provided on the load-up side discharge passages 8a and 8b. It can be adjusted to an appropriate speed according to the high and low differential pressure.

According to the third aspect of the invention, when the high and low differential pressure fluctuates, the communication opening degree of the load-up side discharge passage 8 can be automatically adjusted by the operation of the valve body 84, and the operation of the valve itself. Thus, the load-up speed of the slide valve 3 can be automatically set to an appropriate speed according to the high and low differential pressure.

According to the fourth aspect of the invention, the opening degree of the communication of the load-up side discharge passage 8 can be continuously adjusted by the motor-operated valve MV, and the load-up speed of the slide valve 3 is set to an appropriate speed according to the high and low differential pressure. It can be finely controlled.

According to the fifth aspect of the present invention, the first valve control mechanism 80 can properly control the load-up speed, and the second valve control mechanism 90 also controls the speed at the time of load-down according to variations in the high and low differential pressure. It can be controlled properly.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The refrigerator shown in FIG. 1 is a water-cooled condenser 20 for sequentially liquefying a high-pressure gas refrigerant from a discharge side to a suction side of a screw compressor 10 of which capacity is controllable, and a liquid receiver for storing a liquid refrigerant. The refrigerant pipe 6, the expansion valve 40 for decompressing the liquid refrigerant, and the evaporator 50 for evaporating the liquid refrigerant to obtain cold water
They are connected in series via 0.

The casing 1 of the screw compressor 10 is internally provided with a screw rotor 2, and a slide valve 3 is movably arranged on one side in the radial direction thereof. The slide valve 3 controls the capacity by changing the compression start position of the screw rotor 2 by its movement. Its front end face is in the low pressure region LP on the suction side, and its rear end face is in the high pressure region HP on the discharge side. To face. A piston 4 is connected to the rear side of the slide valve 3 via a rod 31, and the piston 4 is arranged in a cylinder chamber 5 provided on one side in the moving direction of the slide valve 3. Rod-side chamber 5 in cylinder chamber 5
An urging member 56, which is composed of a coil spring or the like, is interposed in the apparatus 1 to stabilize the operation of the piston 4. The head-side chamber 52 in the cylinder chamber 5 has a high-pressure introduction hole 5 that is a small hole that communicates with the discharge gas atmosphere in the high-pressure region HP.
3 is open.

The discharge side of the screw rotor 2 is provided with an oil separator 11 for separating lubricating oil from high-pressure discharge gas, and a high-pressure oil having a check valve 61 at the bottom of the oil separator 11. The passage 6 is connected, and the outlet side of the check valve 61 is connected to the rod side chamber 51 via the supply / discharge passage 7. Between the head side chamber 52 and the low pressure region LP, a load down side opening / closing valve SV1 formed of an electromagnetic valve controlled by a valve controller 800.
The discharge path 9 on the load-down side is connected to the load passage.
Each of the passages 6, 7 and 9 is composed of a pipe or the like.

In the above structure, a low resistance body 81 formed of a capillary tube having a short length is interposed in the middle of the high pressure oil passage 6 between the outlet side of the check valve 61 and the low pressure region LP. , A first load-up side discharge passage 8a composed of pipes and the like, and a high-resistance body 82 formed of a long capillary tube in the middle thereof, and a second load-up side discharge passage similarly composed of pipes and the like 8b is connected in parallel. Further, on-off valves SV2 and SV3, which are electromagnetic valves that open and close according to the high and low differential pressure under the control of the valve controller 800, are interposed in the respective discharge paths 8a and 8b. Thus, the valve control mechanism 80 that controls the load-up speed of the slide valve 3 in accordance with the change in the height difference between the suction side and the discharge side of the screw rotor 2 is configured. In addition, in order to change the flow resistance of the discharge paths 8a, 8b on the load-up side,
Each of the resistors 81 and 82 may be formed of a capillary tube having a different diameter, or the discharge passages 8a and 8b themselves may have different pipe lengths.

The valve controller 800 includes the on-off valves S
V1, SV2, and SV3 are controlled to be opened and closed, and are configured by using, for example, a microcomputer, and the cold water temperature detector 57 of the evaporator 50 and the discharge side of the compressor 10 are provided on the input side thereof. High pressure detector 12 to be provided, and
The low pressure detector 13 provided on the suction side of the compressor 10 is connected.

Thus, the load-up operation of opening the on-off valve SV2 or SV3 on the load-up side and the load-down operation of opening the on-off valve SV1 on the load down side are switched based on the cold water temperature. When the differential pressure is small in response to the change in pressure, only the low resistance side opening / closing valve SV2 is opened, and the oil is discharged through the first load-up side discharge passage 8a. Only the opening / closing valve SV3 on the resistance side is opened, and oil is discharged through the second load-up side discharge passage 8b to control the load-up speed.

Therefore, at the time of load-up, when the high and low differential pressure is small, it is possible to improve the drainage of oil from the rod side chamber 51, and it is possible to prevent malfunction of load-up and delay of load-up time. When the high and low differential pressure is large, it is possible to prevent the load-up speed from becoming too fast.

When the differential pressure is small during load-up, the two load-up side open / close valves SV2 and SV3 are provided.
May be opened together, or the open / close valve SV3 provided on the high resistance side may be omitted, and the open / close valve SV2 on the low resistance side may be opened when the high / low differential pressure is small, and the open / close valve may be opened when the high / low differential pressure is large. The SV2 may be closed. Further, the load-up side discharge passages 8a and 8b are not limited to two, but three or more may be provided. In this case, it is possible to finely respond to fluctuations in high and low differential pressure.

FIG. 2 shows a second embodiment of the valve control mechanism 80.
Is provided in the middle of the load-up side discharge passage 8, one end side communicates with the discharge side of the screw rotor 2 and the other end side communicates with the suction side of the screw rotor 2, and the difference between the suction side pressure and the discharge side pressure is It is configured by a differential pressure valve having a valve body 84 that operates by pressure and adjusts the communication opening degree of the discharge passage 8. Disc 84
Is installed in a valve box 81 having five ports a, b, c, d and e, and is of a spool type having a high pressure land 82 on which the discharge side pressure acts and a low pressure land 83 on which the suction side pressure acts. The low-pressure land 83 is provided with a valve spring 85 such as a coil spring. Two inlet side discharge passages 8c and 8d in which resistor bodies 183 and 184 such as capillary tubes are respectively inserted are connected to a pair of ports c and d provided on the left and right sides of the valve box 81, and
One outlet side discharge passage 8e in which an opening / closing valve SV4 that opens at the time of load-up is provided in a port e provided on the other side of the valve box 81
Are connected. A high pressure introducing passage 86 extending from the gas region of the oil separator 11 is connected to the port a provided at the lower portion of the valve box 81, and a low pressure introducing passage 87 extending from the low pressure region LP is connected to the port b provided at the upper portion of the valve box 81. Are connected.

In this way, when the on-off valve SV4 is opened and the load is increased, and when the height differential pressure is small, the valve element 84 is brought into the state of FIG. 2 by the urging force of the valve spring 85, and the two discharge passages 8c on the inlet side are provided. , 8d, the oil is drained, and the flow resistance is reduced, so that it is possible to prevent malfunction of load-up and time delay. On the other hand, when the height difference is large, as shown in FIG. 3, the valve element 84 moves upward against the valve spring 85, and only the upper port c is opened and the lower pot d is closed. The oil escapes through only one discharge passage 8c, and the flow resistance increases, so that the load-up speed can be prevented from becoming too fast. The resistors 18 shown in FIGS.
3, 184 may have the same resistance value, or the upper side 183
The resistance may be increased with respect to the lower side 184.

In the third embodiment shown in FIG. 4, the flow resistance of one discharge passage 8 on the load-up side is continuously changed by the moving stroke of the valve body 84.
Is housed in a valve box 810 having four ports a, b, e, f, has a high pressure land 820 and a low pressure land 830, and has a low pressure land 8 like the one shown in FIGS.
A valve spring 850 is attached to 30. When the on-off valve SV4 is opened and the load is increased, when the high and low differential pressure is small, the opening of the ports e and f connecting the load-up side discharge passage 8 is increased by the high-pressure land 820 to reduce the flow resistance. However, when the height differential pressure is large, the openings of the ports e and f are reduced to increase the flow resistance.

The fourth embodiment shown in FIG. 5 is a valve control mechanism 80.
Is constituted by an electric valve MV interposed in the discharge passage 8 on the load-up side, and the opening degree of the electric valve MV is continuously adjusted according to the fluctuation of the height difference pressure. In the thing, fine control can be performed.

The fifth embodiment shown in FIG. 6 eliminates not only the load-up speed but also the fluctuation of the load-down speed due to the high / low differential pressure. A first valve control mechanism 80 similar to that shown in FIG. 1 for controlling the load-up speed of the slide valve 3 according to the change in the differential pressure is provided, and the change in the differential pressure between the suction side and the discharge side of the screw rotor 2 is changed. A second valve control mechanism 90 for controlling the load-down speed of the slide valve 3 is provided. When the second valve control mechanism 90 has a large height differential pressure at the time of load down, the force applied to the load up side based on the height differential pressure acting on the front and rear end surfaces of the slide valve 3 becomes large, and the load down speed becomes slow. To correct the

Specifically, the second valve control mechanism 90 is connected in parallel with the first load-down side discharge passage 9a having a high resistance body 91 made of a long capillary tube or the like, and has a length of Consists of a second load-down side discharge passage 9b having a low resistance body 92 composed of a short capillary tube and the like, and on-off valves SV11, SV12 which are respectively installed in these discharge passages 9a, 9b and which open and close according to the high and low differential pressure. To do.

When the differential pressure is small at the time of load down, only the open / close valve SV11 on the high resistance side is opened,
The head-side chamber 52 through the first load-down side discharge passage 9a
Is opened to the low pressure side. On the other hand, when the high and low differential pressure is large, the opening / closing valve SV12 on the low resistance side is opened, and the head side chamber 52 is opened to the low pressure through the second load down side discharge passage 9b. Therefore, when the differential pressure is low, the load down speed can be appropriately adjusted, but when the differential pressure is high, the pressure drop in the head side chamber 52 can be promoted, and the delay in the load down speed can be eliminated.

[0033]

As described above, according to the first aspect of the present invention, the valve control mechanism 80 controls the load-up speed of the slide valve 3 according to the change in the height difference between the suction side and the discharge side of the screw rotor 2. Since it controls, it is possible to obtain an appropriate load-up speed, prevent malfunction of load-up and delay in load-up time when the high-low differential pressure is small, and load-up when the high-low differential pressure is large. It is possible to prevent the speed from becoming too fast, to secure an appropriate control speed in a wide operating range where the high and low differential pressure fluctuates, and to perform an appropriate load-up regardless of the cooling water temperature at the time of starting. .

According to the second aspect of the present invention, the valve control mechanism 80 can be inexpensively constructed by the plurality of load-up side discharge passages 8a and 8b having different flow resistances and the on-off valves SV2 and SV3.

According to the third aspect of the present invention, the load-up speed can be automatically adjusted by the valve element 84 in accordance with the fluctuation of the high and low differential pressure.

According to the invention of claim 4, the motor-operated valve MV
Thus, the control by the valve control mechanism 80 can be finely performed.

According to the invention of claim 5, not only the adjustment of the load-up speed by the first valve control mechanism 80 but also the fluctuation of the load-down speed due to the high and low differential pressure is eliminated by the second valve control mechanism 90. be able to.

[Brief description of drawings]

FIG. 1 is a piping diagram showing a first embodiment of the present invention.

FIG. 2 is a piping diagram showing a low differential pressure of the second embodiment.

FIG. 3 is a main part drawing showing a high differential pressure of the second embodiment.

FIG. 4 is a main part drawing showing the third embodiment.

FIG. 5 is a main part drawing showing the fourth embodiment.

FIG. 6 is a piping diagram showing the fifth embodiment.

FIG. 7 is a piping diagram showing a conventional example.

FIG. 8 is a characteristic diagram of high / low differential pressure vs. load-up time for explaining conventional problems.

[Explanation of symbols]

1; casing, 2; screw rotor, 3; slide valve, 4; piston, 5; cylinder chamber, 7; supply / discharge passage, 8,
8a, 8b; discharge path on the load-up side, 80; valve control mechanism, 84; valve body, MV; electric valve, 90; second valve control mechanism

Claims (5)

[Claims] 1. A slide valve (3) arranged in a casing (1) accommodating a screw rotor (2), a piston (4) connected to this slide valve (3), and an interior of this piston (4). A cylinder chamber (5) for supplying and discharging a high pressure fluid for discharge to and from the cylinder chamber (5), and supplying and discharging the high pressure fluid to and from the cylinder chamber (5). A displacement control device for a screw compressor, which controls a displacement by moving a slide valve (3) connected to the piston (4), wherein the screw rotor (2)
Capacity control of the screw compressor, which is provided with a valve control mechanism (80) for controlling the load-up speed of the slide valve (3) according to the change in the high and low differential pressure between the suction side and the discharge side apparatus. 2. The valve control mechanism (80) is provided in each of the plurality of load-up side discharge passages (8a, 8b) having different flow resistances and these discharge passages (8a, 8b), respectively, and responds to high and low differential pressures. The capacity control device for a screw compressor according to claim 1, which comprises an on-off valve (SV2, SV3) that opens and closes by means of. 3. The valve control mechanism (80) is interposed in the middle of the load-up side discharge passage (8), one end side of which communicates with the discharge side of the screw rotor (2), and the other end side of which is the screw rotor (8). A differential pressure valve having a valve body (84) communicating with the suction side of 2), operating at a pressure difference between the suction side pressure and the discharge side pressure, and adjusting the communication opening of the discharge passage (8). 1. The capacity control device for the screw compressor according to 1. 4. The capacity control device for a screw compressor according to claim 1, wherein the valve control mechanism (80) is composed of an electric valve (MV) provided in the load-up side discharge passage (8). 5. A slide valve (3) arranged in a casing (1) accommodating a screw rotor (2), a piston (4) connected to the slide valve (3), and an interior of the piston (4). A cylinder chamber (5) for supplying and discharging a high pressure fluid for discharge to and from the cylinder chamber (5), and supplying and discharging the high pressure fluid to and from the cylinder chamber (5). A displacement control device for a screw compressor, which controls a displacement by moving a slide valve (3) connected to the piston (4), wherein the screw rotor (2)
Is provided with a first valve control mechanism (80) for controlling the load-up speed of the slide valve (3) according to the change in the height difference between the suction side and the discharge side of the screw rotor (2). The capacity of the screw compressor, which is provided with a second valve control mechanism (90) for controlling the load-down speed of the slide valve (3) according to the change in the high-low differential pressure between the suction side and the discharge side. Control device.