JPH021998B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a device for changing the opening degree of a discharge port of a screw compressor and controlling the capacity thereof.

(Prior Art) A conventional device for changing the opening degree and controlling the capacity of the discharge port of a screw compressor is disclosed in Japanese Patent Application Laid-Open No. 126589/1989. The capacity and pressure ratio can be adjusted by three valves in the target valve member, and the structure is complex and the adjustment is not easy. Also,
In the slide valve described in JP-A No. 51-43211, the slide valve consists of a variable discharge pressure valve and a variable capacity valve, and the variable capacity valve is fitted so as to be able to slide into the small diameter portion of the variable discharge pressure valve. The variable discharge pressure valve and the variable capacity valve slide as a unit, and the two piston rods are not arranged in series on the same axis. Moreover, it cannot be operated by a signal generated by calculating the optimal value of the design volume ratio that provides the minimum required power with respect to the ratio of the discharge pressure to the suction pressure.

Furthermore, the specification and drawings attached to the application of Utility Model Application No. 55-88704 (publication of Utility Model Application No. 57-13896) show that the slide valve is a "fixed valve and a movable valve that fit together". By sliding both valves relative to each other, the length of the slide valve itself can be changed and the internal volume ratio can be changed. Because they are slidably inserted, a small-diameter step is created between the fixed valve and the movable valve, and the length of this small-diameter step changes as the internal volume ratio changes (both As the valves move relative to each other), compressed air leaks into other tooth space through the small diameter step. Therefore, it is actually difficult to form a compression space in such a slide valve.

(Problems to be Solved by the Invention) The present invention eliminates the drawbacks of the prior art, has a simple structure, is easy to adjust, and has an optimal design capacity according to operating conditions (changes in the compressor). The present invention relates to a device that can freely change the design capacity ratio during operation so that the ratio can be obtained.

[Structure of the invention]

(Means for Solving the Problems) The present invention is configured as follows in order to solve the above problems.

A screw compressor having a pair of male and female threaded rotors that mesh with each other, a casing that houses the rotors and forms a tooth space, and both end faces that include a suction port and a discharge port, the screw compressor facing the meshing position of the male and female threaded rotors. a first slide valve in which a recessed groove is formed in the inner wall of the casing to pass through an end face on the suction port side and an end face on the discharge port side in the axial direction, and a part of the inner wall of the cylinder is formed in the recessed groove in a direction parallel to the axis; second slide valves are provided in series on the same axis, the first slide valve is on the discharge port side, the first slide valve and the second slide valve are located on the same axis, and each has a connecting rod; Hydraulic pistons fixed to the connecting rods are operable coaxially within the same hydraulic cylinder, and by independently sliding the first slide valve, the displacement can be controlled, and the discharge A device that senses pressure Pd and suction pressure Ps, and a signal from the sensing device determines the operating compression ratio.
and a regulator that generates a signal by calculating the optimal value of the design volume ratio that provides the minimum required power for Pd/Ps, and the signal from the regulator is used to control the first and second slides. A device for changing the opening degree of a discharge port and controlling the capacity of a screw compressor, which is configured to be able to change the opening degree of a discharge port by sliding a valve as one unit.

(Function) By applying appropriate hydraulic pressure to the hydraulic piston through the hydraulic piping to which the hydraulic cylinder is connected, 2.
The opening degree of the discharge port can be changed easily and reliably by sliding the two slide valves as one body rather than as separate pieces back and forth in the axial direction. Capacity can be controlled by sliding back and forth.

In addition, the suction pressure and discharge pressure are sensed by the suction pressure sensor and discharge pressure sensor installed in the suction and discharge parts of the screw compressor, and these are sent as electrical signals to the regulator, which then operates the compressor. The optimal value of the design volume ratio that provides the minimum required power for the compression ratio is calculated, and the hydraulic pressure is switched based on the signal to slide the first slide valve and the second slide valve as a unit to adjust the opening of the discharge port. By making this change, the screw compressor can be kept in the optimum operating state at all times in response to changes in operating conditions.

(Example) An example of implementation of the present invention will be explained with reference to the drawings.

Reference numeral 1 denotes a casing, which is a part of the casing 1 and passes through both the end face on the discharge port 16 side and the end face on the suction port 17 side below the position where the male threaded rotor 2 and the female threaded rotor (not shown) mesh. A recessed circular groove 18 is formed, into which the first slide valve 3 and the second slide valve 4 which constitute a part of the inner wall of the cylinder are inserted, and a connecting rod 5 fixed to the first slide valve 3 is inserted. hydraulic piston 8
In addition, a connecting rod 6 fixedly attached to the second slide valve 4 connects the hydraulic piston 7, so that the first slide valve 3 and the second slide valve 4 are coaxial, and the hydraulic piston 7 and the hydraulic piston 8 are coaxial. configured to operate on. The hydraulic pistons 7 and 8 are fitted into the hydraulic cylinder 9 with O-rings, cap seals, etc. on the outer peripheral surface that contacts the inner wall of the same hydraulic piston 9, and are fitted into the hydraulic cylinder 9.
1 and 12 are formed. The hydraulic cylinder 9 has connection holes 13 for hydraulic piping 24, 29, 25, 28,
14 and 15 are perforated, and the pipe 24 or 2
By alternately applying hydraulic pressure from 5 to the connecting holes 13 or 15, the slide valves 3 and 4 can be slid back and forth in the axial direction as a unit (in this case, oil does not enter or exit the space 11), and Switching solenoid valve 2
By closing the slide valve 2, the position of the slide valve 4 is fixed at an arbitrary position, and furthermore, by alternately applying hydraulic pressure to the piping 29 or 28, the slide valve 3 is slid back and forth. It is now capable of functioning as a control device. Also 19
20 is a suction pressure sensor, and 20 is a discharge pressure sensor connected to a regulator (microcomputer controller) 21.
The four-way electromagnetic valves 22 and 27 are also connected to the regulator 21.

Next, the operation of the embodiment will be explained with reference to FIG. The suction pressure Ps and discharge pressure Pd are detected by the suction pressure sensor 19 and the discharge pressure sensor 20 provided at the suction and discharge parts of the screw compressor, and these are sent as electrical signals to the regulator 21 for adjustment. In the device 21, the optimum value of the design volume ratio that provides the minimum required power for the operating compression ratio Pd/Ps is calculated. When using R22 as a refrigerant, Vi=1.0+0.51×
Vi is calculated using the Pd/Ps formula, and the electrical signal is given to the electromagnetic four-way valve 22 to transfer the hydraulic pressure from the oil supply header 23 to the hydraulic cylinder 9 via the piping 24 or 25.
The first and second slide valves 3, 4 are integrally moved forward and backward in the axial direction by releasing oil from the other space into the suction section of the compressor through the piping 26. slide it. This allows the design volume ratio Vi at full load to be converted to an optimal value.

Furthermore, when the suction pressure Ps detected by the suction pressure sensor 19 becomes lower than the set pressure of the regulator 21, the difference is calculated by the regulator 21, and the electromagnetic four-way valve 27 is operated by an electric signal. , piping 2
Hydraulic pressure is applied to the space 12 of the hydraulic cylinder 9 through the pipe 8, while the oil in the space 11 is supplied to the pipe 29 and the pipe 30.
By releasing the pressure to the suction low pressure section through the suction port 16, only the first slide valve 3 is slid in the direction of the discharge port 16, so that the suction pressure Ps returns to the set pressure, and the load is reduced.

Next, when using R22 as a refrigerant, Vi=
The reason why the optimum value is obtained by 1.0+0.51×Pd/Ps will be explained.

Here, R22 is one of the universally used refrigerant number designations, and has the chemical formula CClF ₂ H
(chlorodifluoromethane).

The design volume ratio Vi is determined by the design operating conditions, Vi=Vs/Vd, π=Pd/Ps=(Vs/Vd) ^k =(Vi) ^kwhere , Vi: Design volume ratio π: Design Pressure ratio V: Volume P: Pressure k: Adiabatic index d: Discharge side s: Suction side The coefficient of performance can be improved by correcting Vi under operating conditions outside of the design conditions.

What is the relationship between the operating conditions (Pd/Ps=π) and the optimum Vi for the screw compressor?
Refrigerant R22 per model (160SUD, 160LUD)
I experimented using.

Here, 160SUD means that the rotor diameter is 163.2 mm and the rotor length is 180 mm (displacement amount 413 m ³ /H, that is, length / diameter / = L / D = 1.1.
160LUD has a rotor diameter of 163.2mm and a rotor length.
270mm (referring to the case where the displacement is 619m ³ /H, that is, length/diameter = L/D = 1.65).

In Figures 4 to 6, ηv: Volumetric efficiency = V _R /V _th ηad: Total adiabatic efficiency = Nad/BKW However, BKW (KW): Required power Nad (KW): Adiabatic compression power V _R (m ³ /h): Actual suction amount V _th (m ³ /h): Theoretical displacement amount Figure 4 shows axial Portβ _M = for model 160LUD.
30゜, rotation speed N = 3000rpm, Pd = 15.6Kg/cm ²・a
This is the result of an experiment with different Ps.

In addition, Figure 5 shows the axial
Portβ _M = 30°, rotation speed N = 3000rpm, Pd = 12.9
These are the results of experiments with different Ps at Kg/cm ²・a.

When manufacturing a conventional screw compressor with a fixed design volume ratio Vi, three types of Vi values are prepared to accommodate various suction and discharge pressure conditions. That is, the standard value of Vi is 2.63,
Manufacturers generally prepare three types: 3.65 and 5.80.

Therefore, when the pressure conditions are known in advance depending on the application, the one most suitable for the conditions may be selected from among the three types of Vi values. However, when the pressure conditions under which the screw compressor is operated change (for example, when changing the temperature of a refrigerator or using a heat pump for both cooling and heating), Pd or Ps or Pd and Ps may change. Since Vi fluctuates, the above-mentioned fixed Vi type has many operating regions with poor efficiency, resulting in losses.

When the pressure or operating conditions fluctuate in this way, generally the intermediate value of the above Vi values, "Vi=3.65", is adopted and π=Pd/
There are many cases in which the operating losses for smaller and larger Ps are ignored (conventional technology). This is also the reason why we selected Vi=3.65 as the conventional technology in this experiment.

Figures 4 and 5 show the apparatus of the present invention (Figure 3).
, its electrical control circuit is kept inactive, Pd is fixed constant, Ps is varied, and Vi
When I manually changed the value between 2.2 and 4.5,
This is the performance of the screw compressor, ηv,
The effect on ηad and BKW was confirmed through experiments.

What can be understood from these drawings will be explained using examples. According to Fig. 4, the design volume ratio Vi at which the required power BKW is the minimum value when the suction pressure Ps = 2.5
The optimal value of is 4.2, the optimal value of Vi when Ps = 3.6 is 3.2, the optimal value of Vi when Ps = 5.1 is 2.6, Ps
It can be seen that the optimal value of Vi when = 6.0 is 2.3.

From this, it can be seen that when Pd is constant, the optimal value of Vi changes sequentially as the value of Ps changes.

The same can be said about FIG.

FIG. 6 shows the results of the comparison of the performance of the prior art with Vi=3.65 fixed at Vi=3.65 and the performance of the device of the present invention at the optimum volume ratio, and the results are expressed as improvement rates. The three types of curves were drawn based on the experimental results shown in FIGS. 4 and 5.

Now, of the curves in FIG. 6, how to draw the curve for the total adiabatic efficiency ηad will be explained as an example.

In Figure 4, we consider that the conventional type is fixed at Vi = 3.65, so Vi on the horizontal axis of the figure
Establish a vertical line from the point =3.65 and find the point where this line intersects the curve group of ηad. Since there are four Ps,
Four such intersection points are also found. Now, this perpendicular line and Ps
When we find the intersection with the ηad curve of =5.1, the value can be read as approximately 72 (%) from the scale of the vertical axis. Next, in Fig. 4, considering the Vi variable type, in the curve of required power BKW when Ps = 5.1, the minimum value is at Vi = 2.6 (this is the same as when Pd = 15.6 and Ps = 5.1). In this case, Vi=2.6
This is the optimal value that minimizes BKW).
Therefore, draw a perpendicular line from the point Vi = 2.6 on the horizontal axis,
If we find the point where this line intersects with the ηad curve (Ps = 5.1 curve), the ηad value at this intersection can be read as approximately 79 (%) from the scale of the vertical axis.

Therefore, when the quotient is calculated using 72, which is the ηad value of the fixed Vi type, as the denominator and 79, which is the ηad value of the variable Vi type, as the numerator, it becomes 79/72=1.097≈1.1.
By the way, in the current example, Ps = 5.1, so π =
Pd/Ps=15.6/5.1=3.0.

Therefore, in FIG. 6, draw a perpendicular line from the point π=3 on the horizontal axis, and find a point on this line with a scale of 1.10 on the vertical axis. By repeating the calculation in this way and finding many points, connecting these points with a line will draw the curve of ηad in the same figure.

This is done using the experimental model 160LUD shown in Figure 4, and Pd
= 1.56 is constant and Ps = 5.1, the total insulation efficiency ηad of the variable Vi type is 1.10 compared to the fixed Vi type.
(total insulation efficiency is improved by 10%). ηv and BKW
The curves shown in FIG. 6 can also be drawn using the same method as described above.

Regarding the required power BKW, the Vi fixed type
If the value of BKW is the denominator and the value of BKW of the Vi variable type is the numerator, in Figure 6, π (= Pd / Ps) =
When it is 5.2, the improvement rate is 1, that is, the denominator and numerator values are the same, but this means that in the case of the conventional type where Vi = 3.65 was fixed, π = 5.2 was exactly compatible with the structure of the screw type compressor. Indicates that it is in operation.

However, whether the value of π becomes smaller or larger, the required power BKW is smaller in the Vi variable type, in other words, the value of the numerator/value of the denominator is less than 1. For example, a point on the BKW curve has a value of 0.95 on the vertical axis scale, which means that the point is 5
% (meaning an improvement rate of 0.95).

Figure 7 shows the required power based on the results of the above example.
Find Vi where BKW is the minimum value, that is, the optimal value of Vi.
Pd/Ps (=π) is plotted and an approximate expression (solid line) is obtained from this group of optimum values.

In addition, the broken line in the figure is Pd/Ps=Vi ^k (broken line index,
k=1.184, R22).

Originally, in a positive displacement compressor, assuming that the compression stroke is an adiabatic change, P ₁ V ₁ ^k = P ₂ V ₂ ^k holds, so the volume ratio and pressure ratio are V ₁ /V ₂ = (P ₂ / _P1 ) ^1/k
(=Vi). However, as a result of experiments with an actual screw compressor, the required power
The relationship between the optimal Vi and π (=Pd/Ps) that minimizes BKW is actually as shown in the solid line in Figure 7, and Vi
= (Pd/Ps) It was found that there was a deviation from the broken line obtained from the theoretical formula of ^1/k . By first approximating this solid line obtained from the experiment, Vi=1.0+0.51×Pd/Ps
An approximate expression is obtained.

Therefore, in the case of R22, by this approximation formula,
It can be seen that the optimal value of Vi can be obtained.

〔Effect of the invention〕

The present invention provides a screw compressor in which a recessed groove is formed in the inner wall of the casing facing the meshing position of the male and female screw rotors, and the recessed groove is formed in the axial direction passing through the suction side end face and the discharge side end face, and the recessed groove is formed in the recessed groove. A first slide valve and a second slide valve that form part of the inner wall are provided in series, the first slide valve being on the discharge port side, and the first slide valve and the second slide valve forming a part of the inner wall.
The slide valves are each provided with a connecting rod so as to be located on the same axis, and the hydraulic pistons each fixed to the connecting rod can operate on the same axis within the same hydraulic cylinder. Since the first and second slide valves are configured to be able to slide integrally or independently, the configuration is relatively simple, and the adjustment operation of the slide valves is also easy. By sliding the two slide valves together, the opening degree of the discharge port can be changed to ensure that the optimum design volume ratio according to the operating conditions can always be obtained, and during partial loads, the first slide valve can be operated independently. Capacity can also be easily controlled by sliding it.

Further, in the above configuration, there is provided a regulator that generates a signal by calculating the optimal value of the design volume ratio that provides the minimum required power for the ratio of the discharge pressure Pd and the suction pressure Ps, that is, the operating compression ratio Pd/Ps, and this signal. Since it is equipped with a discharge port opening change mechanism that slides the first and second slide valves as one unit, the discharge port can be adjusted by using the slide valve, which is a combination of a fixed valve and a movable valve that slide relative to each other. Unlike the conventional technology, which attempts to create a compression space, there is no fear of difficulty in forming the compression space, and it is possible to easily obtain the optimal design volume ratio in response to changes in operating conditions, so that the screw compressor can always be operated at the optimal design volume ratio. Can be kept in running condition.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of a screw type compressor portion equipped with first and second slide valves of the present invention, FIG. 2 is an enlarged sectional view of a hydraulic piston portion of the embodiment of FIG. 1, and FIG. The figure is an explanatory diagram of the overall configuration of the device of the present invention equipped with the screw type compressor shown in FIG. 1, and FIGS. 4 and 5 are graphs depicting the results of experiments conducted on two models equipped with the device of the present invention. , FIG. 6, and FIG. 7 are graphs created based on the results of the above experiment. 1...Casing, 2...Male thread rotor, 3...
...First slide valve, 4...Second slide valve, 5,
6... Connecting rod, 7, 8... Hydraulic piston, 9...
Hydraulic cylinder, 16... Discharge port, 17... Suction port, 18... Concave circular groove as a depressed groove, 19... Suction pressure sensor as a device for sensing suction pressure, 20... Device for sensing discharge pressure. discharge pressure sensor, 21...regulator, 2
2, 27... Solenoid four-way valve as a switching solenoid valve,
23... Oil supply header, 24, 25, 26, 28,
29, 30...Piping for forming a hydraulic circuit.

Claims (1)

[Scope of Claims] 1. A screw compressor having a pair of male and female threaded rotors that mesh with each other, a casing housing the rotors and forming a tooth space therein, and both end faces provided with a suction port and a discharge port, wherein the male and female threaded A recessed groove is formed in the inner wall of the casing facing the rotor engagement position, passing through the end face on the suction port side and the end face on the discharge port side in the axial direction, and a part of the inner wall of the cylinder is inserted into the recessed groove in a direction parallel to the axis. A first slide valve and a second slide valve to be formed are provided in series on the same axis, the first slide valve being on the discharge port side, and the first slide valve and the second slide valve being located on the same axis, respectively. A connecting rod is provided, and hydraulic pistons fixed to the connecting rods can operate coaxially within the same hydraulic cylinder, and the capacity can be increased by independently sliding the first slide valve. The operating compression ratio is determined by a device that detects the discharge pressure Pd and suction pressure Ps and a signal from the sensor.
and a regulator that generates a signal by calculating the optimal value of the design volume ratio that provides the minimum required power for Pd/Ps, and the signal from the regulator is used to control the first and second slides. A device for changing the opening degree of a discharge port and controlling the capacity of a screw compressor, which is configured to be able to change the opening degree of a discharge port by sliding a valve as one unit. 2. It has a regulator that inputs an electrical signal from a device that senses the discharge pressure Pd and the suction pressure Ps, calculates the optimal design volume ratio, and generates the electrical signal, and the switching solenoid valve is controlled by the electrical signal from the regulator. Changing the opening degree of the discharge port of the screw compressor according to claim 1, in which the hydraulic piston is operated by switching the hydraulic circuit by operating the hydraulic piston, and the first and second slide valves are slid as a unit; Capacity control device. 3. The screw compressor according to claim 1 or 2, wherein when chlorodifluoromethane is used as a refrigerant, the optimum design volume ratio is calculated by Vi=1.0+0.51×Pd/Ps. Discharge port opening change and capacity control device.