Screw compressor

Abstract

The invention relates to a screw compressor (10), in particular for a refrigeration circuit, comprising:-a containing body (11), which in turn comprises:-a suction chamber (11a) and a suction port (12) for a fluid to be compressed; -a delivery chamber (11b) and a discharge port (13) for the compressed fluid; -a housing seat (14) for the two helical compression rotors (15, 16) placed side by side; -two helical compression rotors (15, 16) placed side by side; -an electric motor (17) for actuating the helical compression rotor (15, 16); -a lubrication device (18) for the helical compression rotors (15, 16); filtering means (19) for compressing the fluid; -a frequency converter (23) connected to the electric motor (17); -an electronic control unit (24) configured to control and manage the frequency converter (23); a low pressure sensor (25) located at the suction port (12) and connected to the electronic control unit (24); a high pressure sensor (26) located at the discharge port (13) and connected to the electronic control unit (24); a regulating valve core (27) configured for regulating the width of the outlet opening (22) of the compression rotor chamber; -fluid actuating means (28) for moving the regulating valve cartridge (27), these fluid actuating means (28) being controlled by an electronic control unit (24); -a current meter (30) configured to measure the current absorbed by said electric motor (17) during operation of the compressor. The control unit (24) is configured to: determine an optimal natural volume ratio (Vi-optimal); -commanding the fluid actuation means (28) such that they move the regulating valve cartridge (27) in a manner that automatically maintains the optimal intrinsic volume ratio (Vi-optimal).

Description

Technical Field

[0001] The invention relates to a screw compressor.

[0002] In particular, the invention relates to a positive displacement compressor provided with a flow regulating device, in particular, to a screw compressor comprising a housing in which a suction chamber provided with a suction valve and a delivery chamber provided with a delivery valve are indicated, between which a set of screw rotors meshing with each other are included. At the bottom of the housing, a lubricating oil collection tank is obtained. Background Art

[0003] Today, known screw-type positive displacement compressors are provided with a flow regulating unit comprising a slide valve cooperating externally with the rotor and actuated by a fluid actuator in a longitudinal direction parallel to the longitudinal axis of the same rotor.

[0004] The fluid actuator has an active chamber which is supplied with oil from a reservoir to slide a plunger placed in the same active chamber and is provided with a rod connecting it to a spool valve.

[0005] In compressors of known type, the jacket and the bottom of the actuator present a plurality of flow passages, to which are connected an equal number of discharge ducts conveying oil from the active chamber of the fluid actuator to the suction chamber of the compressor.

[0006] In particular, each discharge conduit is provided with a flow shut-off valve.

[0007] Therefore, by selectively opening and closing these stop valves, different amounts of oil can be maintained in the active chamber of the fluid actuator to position the plunger and the sliding valve connected thereto at different axial positions relative to the rotor.

[0008] This will split the compressor suction flow and change its flow rate.

[0009] The degree to which the compressor flow is diverted depends on the position of the actuator flow path and the position in which the shutoff valve opens and remains closed.

[0010] All screw compressors, in order to carry out power modulation, that is to say in terms of refrigerant flow, have a mechanical system consisting of a valve core that opens and closes the suction port; the two rotors are involved in the definition of a compression chamber, part of which is movable and when this valve core moves, it causes part of the screw to not be involved with the refrigerant.

[0011] In a screw compressor in which a frequency converter is provided and therefore a drive is provided for controlling the speed of the electric motor actuating the screw rotor, a slide valve for diverting the flow of fluid entering the screw rotor is not required, since the fluid flow rate is reduced by reducing the number of revolutions of the screw rotor; in this type of screw compressor, the chamber formed between the two rotors is closed, and only the discharge port allows the compressed fluid to leave the screw rotor.

[0012] The pressure on the discharge side, ie at the screw rotor outlet opening, depends on the pressure of the circuit in which the compressor is inserted, which in turn depends on the ambient conditions, the type of circulating fluid, and other factors depending on the refrigerant and the conditions in which it operates in terms of temperature and pressure.

[0013] Therefore, there is a huge variability in the conditions required to operate a typically identical screw compressor.

[0014] Typically, customers who purchase screw compressors inform the manufacturer about the operating conditions of the screw compressors.

[0015] Therefore, since the inlet opening and the outlet opening of the compression screw rotor are fixed, the output pressure required by the system in which the compressor is inserted can be obtained only by changing the speed of the electric motor.

[0016] However, in this way, in order to prevent the compressor from working inefficiently, ie with high consumption, it is necessary to manufacture a compressor with an outlet opening custom designed and manufactured for the specific application.

[0017] However, this entails a high cost to the purchaser, since the compressor must be adapted to the specific application in the specific system, and this adaptation is achieved by performing specific machining operations on the compressor itself, usually at the discharge opening of the screw rotor. Summary of the invention

[0018] The task of the present invention is to develop a screw compressor capable of eliminating the aforementioned disadvantages and limitations of the prior art.

[0019] In particular, one object of the present invention is to develop a screw compressor capable of performing the necessary and sufficient work required in the system in which the same screw compressor is inserted, without requiring additional energy consumption and under a wider range of operating conditions.

[0020] Another object of the present invention is to develop a screw compressor capable of minimizing its own energy consumption.

[0021] The above-mentioned tasks and objects are achieved by a screw compressor according to claim 1 .

[0022] Further features of the compressor according to claim 1 are described in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above tasks and objects as well as the advantages which will be mentioned below will be indicated by the description of an embodiment of the invention given by way of non-limiting example with reference to the accompanying drawings, in which:

[0024] - Figure 1 A perspective sectional view showing a screw compressor according to the present invention;

[0025] - Figure 2 A schematic diagram showing a screw compressor according to the present invention;

[0026] - Figure 3 A first block diagram showing a method for operating a screw compressor according to the present invention;

[0027] - Figure 4 A second block diagram showing a method for operating a screw compressor according to the present invention;

[0028] - Figure 5 A third block diagram shows the operating method of a screw compressor according to the present invention. DETAILED DESCRIPTION

[0029] With reference to the above-mentioned drawings, a screw compressor according to the present invention, in particular a screw compressor for a refrigeration circuit, is generally indicated by numeral 10.

[0030] The screw compressor 10 comprises:

[0031] - A housing body 11, which in turn comprises:

[0032] - a suction chamber 11a and a suction port 12 for the fluid to be compressed;

[0033] - a delivery chamber 11 b and a discharge port 13 for said compressed fluid;

[0034] a housing seat 14 configured to accommodate two screw compression rotors 15 and 16 placed side by side, the housing seat 14 being interposed between the suction chamber 11a and the discharge chamber 11b; the housing seat 14 comprising an inlet opening 21 and an outlet opening 22 for the fluid;

[0035] - two helical compression rotors 15 and 16 placed side by side, each of the two helical compression rotors 15 and 16 having a helical protrusion configured to engage with a helical protrusion of the other compression rotor to define one or more compression chambers for the fluid;

[0036] - an electric motor 17 for actuating the screw compression rotors 15, 16;

[0037] - a lubricating device 18 with a lubricating fluid for the screw compression rotors 15, 16;

[0038] - a filter device 19 for the compressed fluid, the filter device 19 being used to separate the lubricating fluid from the compressed fluid;

[0039] - a frequency converter (converter) 23 connected to the electric motor 17;

[0040] - an electronic control unit 24 configured to control and manage the frequency converter 23;

[0041] The special features of the screw compressor 10 also include:

[0042] a low pressure sensor 25 positioned at said suction port 12 and connected to the electronic control unit 24 ;

[0043] a high pressure sensor 26 positioned to measure the pressure of said discharge port 13 and connected to the electronic control unit 24 ;

[0044] an adjusting valve core 27 which is configured to adjust the width of the outlet opening 22;

[0045] - a fluid actuating device 28, which is configured to move the regulating valve core 27, and the fluid actuating device 28 is controlled by the electronic control unit 24;

[0046] An ammeter 30 configured to measure the current absorbed by said electric motor 17 during operation of the compressor, this ammeter 30 being connected to the electronic control unit 24 .

[0047] Specifically, the control unit 24 is configured as follows:

[0048] - measuring the outlet pressure Hp by means of the high pressure sensor 26 and measuring the inlet pressure Lp by means of the low pressure sensor 25;

[0049] - calculating the compression ratio Pr between the outlet pressure Hp and the inlet pressure Lp;

[0050] - measuring the current Ivi absorbed by the electric motor 17;

[0051] - controlling the fluid actuating device 28 so as to move the regulating valve element 27 to a position in which the current Ivi absorbed by the electric motor 17 is as low as possible according to the compression ratio Pr;

[0052] - Determine the optimal inherent volume ratio Vi -最佳, i.e. the inherent volume ratio corresponding to the position of the regulating valve core 27, which determines the minimum absorption Ivi-min of the current absorbed by the electric motor 17;

[0053] - regularly or continuously measuring the rotation speed W of the electric motor 17, and regularly or continuously measuring the outlet pressure Hp and the inlet pressure Lp, so as to regularly calculate the compression ratio Pr;

[0054] - command the fluid actuator 28 so that the fluid actuator 28 automatically maintains the optimal inherent volume ratio Vi -最佳 The regulating valve core 27 is moved in a manner.

[0055] As is well known in the art, the term "intrinsic volumetric ratio" refers to the ratio between the volume of gas sucked into the compressor and the volume of the same amount of gas when discharged.

[0056] In a non-limiting embodiment of the present invention, the fluid actuation device 28 includes an oil-actuated actuator 34 having a stem 35 attached to the regulating valve spool 27 .

[0057] The oil-operated actuator 34 comprises:

[0058] - a piston 36 fixed to the rod 35;

[0059] a first chamber 37 configured to receive pressurized oil in order to push the piston 36 in a first direction, thereby actuating the regulating valve spool 27;

[0060] A second chamber 38 in which there is a counter-thrust device configured to push the piston 36 in a second actuation direction of the regulating valve element 27 opposite to said first actuation direction.

[0061] The reverse thrust device is constituted by a coil spring 39 , for example.

[0062] The fluid actuation device 28 further comprises:

[0063] - a pressurized oil loading line 40 configured for the passage of oil from the collecting tank 18 a to the first chamber 37 ;

[0064] - a discharge line 41 configured as a passage for oil from the first chamber 37 to the suction chamber 11 a ; the suction chamber 11 a is at low pressure;

[0065] - a first one-way solenoid valve 42 for opening the loading line 40;

[0066] - a second one-way solenoid valve 43 for opening the discharge line 41;

[0067] The first one-way solenoid valve 42 and the second one-way solenoid valve 43 are commanded by the electronic control unit 24 .

[0068] In an embodiment of the present invention, which does not limit the present invention, the loading line 40 and the discharge line 41 are connected at a two-way section 44, which is directly connected to the first chamber 37 of the oil-powered actuator 34, such as Figure 2 A collecting sump 18a is located in a known manner below the screw rotors 15 and 16 and is connected to the conveying chamber 11b.

[0069] A method for operating such a screw compressor 10 is also an object of the present invention; Figure 3 , 4 and 5 are schematically shown.

[0070] This method is understood to be applied with the aid of a driver, wherein the term "driver" refers to a set of software programs that enable the operating system to drive a hardware device.

[0071] The operation method comprises a first step (in Figure 3 100): Automatically search for the optimal inherent volume ratio Vi -最佳 .

[0072] The first step 100 includes the following steps:

[0073] - Make the electric motor 17 reach a preset minimum speed nr-min2; This minimum speed nr-min2 can be set to a value between 1200rpm and 2400rpm, for example 2000rpm; This first operation step is Figure 3 Schematically shown by box 101;

[0074] - Maintain the minimum speed nr-min2 for a period of time, for example, a period of time between 10 seconds and 90 seconds, for example, 20 seconds; this time interval is called the "thermodynamic stability time" T_nr-min2; the second operation step is Figure 3 Schematically shown by box 102;

[0075] - Start searching for the optimal intrinsic volume ratio Vi -最佳 ; At startup, the piston of the fluid actuator is in a starting position with a minimum outlet opening, and the inherent volume ratio Vi corresponds to the starting position, for example, Vi = 4.4; the third operation step is Figure 3 Schematically shown by box 103;

[0076] -Measure Hp and Lp, calculate Pr and store Pr; store Pr for subsequent Vi -最佳 The fourth operation step is Figure 3 Schematically shown by box 104;

[0077] At the same time, the current Ivi absorbed by the electric motor 17 at the start of the search is measured. 开始 , and store Ivi- 开始 ; This fifth operation step is Figure 3 Schematically shown by box 105;

[0078] - In time interval T -打开A The regulating valve core 27 is enabled to move for the first time within the sixth operation step schematically represented by frame 106, which enables it to move from the starting position with the smallest outlet opening and move towards the position with the largest outlet opening, and this seventh movement step is schematically represented by frame 107; time interval T- 打开 A can be set between 20 seconds and 90 seconds, for example, preferably 60 seconds;

[0079] - During the first movement of the regulating spool 27, the value of the absorbed current Ivi is measured and the minimum value Ivi of this absorbed current is stored -低 ; The eighth operation step is Figure 3 Schematically shown by box 108;

[0080] - The value Ivi of the current absorbed at the end of the movement of the regulating valve core 27 is measured and stored -结束 ; The ninth operation step is Figure 3 Schematically shown by box 109;

[0081] In the time interval T- 打开 B enables the regulating valve core 27 to move a second time, such as Figure 3 The frame 110 in FIG. 1 schematically shows that the regulating valve core 27 moves from the position reached by the first movement to the starting position with the minimum outlet opening; the time interval T- 打开 B is at most 60 seconds; the eleventh step related to the second movement is schematically shown by box 111;

[0082] During the second movement of the regulating spool 27, the value of the absorbed current is measured and is denoted Ivi -最佳 ; The thirteenth operation step is Figure 3 Schematically shown by box 112;

[0083] - The following evaluation steps schematically illustrated by block 113 are performed:

[0084] -If Ivi -最佳 Roughly equivalent to Ivi -低 , unless the variable Delta-I appears, that is, if

[0085] Ivi -低 - Delta-I<Ivi-最佳 <Ivi -低 + Delta-I,

[0086] For Vi -最佳 The search is ended; the fourteenth step is schematically shown by box 114;

[0087] - Otherwise, we return to the initial step, box 101, where the electric motor 17 is at a preset minimum speed nr-min2. -低 If the current drawn at the starting point of the first movement and the second movement falls below a predetermined parameter value, a possible fault is signaled.

[0088] Once the inherent volume ratio Vi is determined -最佳 The compressor operation method includes a second step 200, which includes a second set of operations to automatically control and maintain the optimal value of Vi -最佳 .

[0089] Vi -最佳 This set of automatic control and maintenance operations includes the following operating steps:

[0090] - Check whether the current rotation speed nr of the electric motor 17 is stable, i.e., evaluate whether the following is true:

[0091] nr -先前 -Δnr <nr<nr -先前 +Δnr

[0092] In the reading time period Delta-T,

[0093] in:

[0094] nr is a numerical value and corresponds to the current speed;

[0095] nr -先前 is numerical and corresponds to the rotation speed previously considered to be stable;

[0096] Δnr is a constant and corresponds to the reading tolerance of the current speed (2×Δnr=dead zone);

[0097] This step is Figure 4 Schematically shown by box 201;

[0098] - if the current speed nr is unstable, return to the same initial step of checking the current speed nr;

[0099] If the current speed nr is stable, then, as shown in block 202:

[0100] nr -先前 =nr

[0101] Then:

[0102] - Check if the current compression ratio Pr is different from the previous value Pr -先前 ; This step is Figure 4 This is schematically shown by box 203; this checking step involves performing the following checks:

[0103] Pr -先前 -DPr <Pr<Pr -先前 +DPr

[0104] In the reading time period Delta-T,

[0105] in:

[0106] Pr is a numerical value and corresponds to the current compression ratio;

[0107] P -先前 is numerical and corresponds to the compression ratio previously considered stable;

[0108] DPr is a constant and corresponds to the reading tolerance of the current compression ratio (2×ΔPr=dead zone);

[0109] - if the current compression ratio Pr is not different, return to the initial step of checking the current speed nr;

[0110] - If the current compression ratio Pr is different from the previous value P -先前 , then establish

[0111] Pr -先前 =Pr;

[0112] This step is schematically illustrated by box 204;

[0113] -establish

[0114] I -先前 =I

[0115] in

[0116] I is a numerical value and corresponds to the current value currently absorbed;

[0117] I -先前 is numerical and corresponds to the value of current absorbed that was previously considered to be stable;

[0118] This step is schematically illustrated by box 205;

[0119] Therefore, the method involves searching for the optimal intrinsic volume ratio Vi -最佳 The new value of .

[0120] Therefore, the method 200 comprises the following steps:

[0121] - Check whether the conditions are applicable:

[0122] Dir=A

[0123] Where "Dir" is a Boolean variable whose allowed values ​​are:

[0124] “A”, where A corresponds to the direction of movement of the piston 36 by opening the first solenoid valve 42 and therefore also to the direction of movement of the regulating spool 27 which will increase the outlet opening 22;

[0125] “B”, where B corresponds to the direction of movement of the piston 36 by opening the second solenoid valve 43 and therefore to the direction of movement of the regulating spool 27 which will reduce the outlet opening 22;

[0126] This step is schematically illustrated by box 206;

[0127] - if “Dir=A” is not applicable (block 207 ), then the regulating valve element 27 is moved towards the maximum opening position of the outlet opening 22 by energizing the first solenoid valve 42 for a time interval Dt-energizing-A (block 209 );

[0128] - if “Dir=A” applies (block 208 ), then the regulating valve element 27 is moved towards the minimum opening position of the outlet opening 22 by energizing the second solenoid valve 43 during the time interval Dt-energizing-B (block 210 );

[0129] - Check if the current I currently absorbed is lower than the previous value of the current absorbed I -先前 :

[0130] I<I -先前

[0131] This step is schematically illustrated by box 211;

[0132] If the current I currently absorbed is lower than the value of the current I previously considered to be stable -先前 , then detect whether the following conditions apply, as schematically shown in block 212:

[0133] Dir=A

[0134] If the condition Dir=A is not satisfied, then at block 213 , the regulating valve core 27 is moved to the maximum opening position of the outlet opening 22 by energizing the first solenoid valve 42 .

[0135] If the condition Dir=A occurs, then at block 214 , the regulating valve element 27 is moved to the minimum opening position of the outlet opening 22 by energizing the second solenoid valve 43 .

[0136] After one of the two optional steps of moving the regulating valve core 27,

[0137] Perform the following steps:

[0138] - As shown in block 215, the value I of the current currently absorbed is saved as the value I of the current previously absorbed -先前 ;

[0139] - Check that the current speed nr is stable, i.e. evaluate whether the following is true:

[0140] nr 先前 -Dnr<nr<nr 先前 +Dnr

[0141] In the reading time period Delta-T; this step is schematically shown by box 216;

[0142] - If the current rotation speed nr is unstable, return to the initial step of checking the current rotation speed nr mentioned in box 201;

[0143] - If the current speed is stable, save the current value I absorbed as the previous current value I absorbed -先前， As shown in block 205, the process returns to block 206 to check the condition "Dir=A".

[0144] If, with respect to the check step schematically shown in block 211 , the currently absorbed current I is not lower than the previous value of the absorbed current I -先前 ,but:

[0145] - Check if the current I currently absorbed is greater than the previous value of the current absorbed I -先前 , as schematically shown in block 217;

[0146] - If the current absorbed current I is greater than the previous absorbed current value I -先前 , then the current absorbed current value I is saved as the previous absorbed current value I -先前 , as described above for block 215 , and checking that the current speed nr is stable, as described for block 216 ;

[0147] - If the current absorbed current I is not greater than the previous value of the absorbed current I -先前 , then the current compression ratio Pr value is saved as the previous compression ratio value Pr -先前 , and returns to the beginning, ie the initial step, as described above in box 201.

[0148] The initial startup steps before the first step 100 are as follows Figure 5 It is schematically shown in FIG. 1 and is indicated by the number 300 therein.

[0149] The initial startup step 300 includes:

[0150] - a start-up operation, as shown in box 301 , in which the electric motor 17 is switched on and reaches a minimum speed nr-min1; this operation is schematically shown in box 302 ;

[0151] - a waiting period for checking the status of the sensor and the alarm connected thereto; this operation is schematically illustrated by box 303;

[0152] The operation of the first step 100 is activated, in which the electric motor 17 is operated at a rotational speed nr-min2; this operation is schematically indicated by a block 304 .

[0153] Figure 5 The diagram in embodies both the possibility that the operating method includes the above-mentioned second step 200 and the possibility that the operating method does not include the second step 200 or the second step 200 is disabled.

[0154] Basically, the algorithm checks the rotation speed nr of the screw compressor 10 at regular intervals (for example 60 seconds); in case of a constant rotation speed nr between the readings, the electronic control unit 24 checks the compression ratio Pr.

[0155] The algorithm then also controls the compression ratio Pr.

[0156] After verifying the regularity of the compression ratio Pr over time, the algorithm resumes control of the speed nr; conversely, after verifying the variation of the compression ratio Pr, the electronic control unit 24 is activated to search for the optimal inherent volume ratio Vi -最佳 .

[0157] By controlling the compression ratio Pr, the electronic control unit 24 determines whether to activate the first (charge) solenoid valve 42 or the second (discharge) solenoid valve 43 .

[0158] After each actuation period (which itself consists of a valve activation period plus a waiting period), the algorithm checks the new value of the current I absorbed by the electric motor 17 .

[0159] The algorithm continues to operate the solenoid valves 42 and 43 to reduce the value I of the current absorbed by the electric motor 17 , ie the current I delivered to the electric motor 17 by the frequency converter 23 , until the value I of the absorbed current increases.

[0160] After a series of decreasing values, the increase in the absorbed current I indicates that the current delivered by the frequency converter 23 reaches a minimum value and therefore reaches Vi -最佳 , where Vi -最佳 Corresponding to the optimal position of the regulating valve core 27.

[0161] In this case, the algorithm exits the control step and sets the measured compression ratio Pr as the new reference compression ratio.

[0162] The invention therefore develops a screw compressor 10 and a method for operating such a screw compressor which allows to optimize the efficiency of the screw compressor 10 itself by operating the electronic components so that all electrical absorptions are always in real time in order to minimize them.

[0163] Today, screw compressor manufacturers rely on information from buyers that is often inaccurate and often not exchanged in the required format that meets manufacturer requirements.

[0164] Once the screw compressor according to the present invention is inserted into the system, it will reach a stable speed proportional to the power required by the system; at startup, the regulating valve core of the screw compressor is in a certain position, and it is not yet known whether it is right or wrong, but due to the two solenoid valves, the electronic control unit begins to move the regulating valve core independently, and uses the above-mentioned operating method to analyze whether the current absorbed under the same stability conditions is decreasing or increasing; under stable conditions, it has the ability to work with the current absorbed by the electric motor, and the system self-regulates by adjusting the optimal position of the valve core to obtain the lowest absorbed current.

[0165] Therefore, the minimum current draw is sought when the input and output pressures remain constant and the speed is constant.

[0166] Thus, the screw compressor according to the invention can be operated under optimal conditions, wherein "optimal conditions" are defined as conditions under which safe operation of the compressor occurs within its envelope, ie a set of boundary conditions approved by the manufacturer, and with minimum current absorption.

[0167] The screw compressor according to the invention, through its operating method, is able to operate with automatic regulation of the inherent volume ratio Vi, which is defined by the ratio between the volume of gas sucked into the compressor and the volume of the same amount of gas when it is discharged during operation, with all the advantages brought about by the possibility of modifying the screw compressor Vi, which are well known in air-conditioning applications, process cooling and heat pumps.

[0168] The screw compressor according to the invention with an integrated frequency converter therefore results in a particularly complex solution for achieving an automatic variation of Vi, for example within a value range of 2.2 to 4.4.

[0169] This algorithm, managed by the electronic control unit of the inverter itself, allows for constant monitoring of the compressor operating conditions and modifies the compressor's Vi accordingly.

[0170] The end result of this process is that the compressor continuously adapts its Vi to the exact operating conditions of the chiller, always operating at the highest possible efficiency level.

[0171] The screw compressor according to the present invention is particularly useful in applications where the operating conditions of the compressor itself, indicated by the suction pressure and the discharge pressure, vary significantly over time, such as in a reversible heat pump, resulting in a significant increase in average seasonal efficiency parameters such as SEPR, SEER, SCOP, where SEPR is an energy indicator for cooling, but only for water cooling, not for air cooling, and only for industrial chillers, SEER is an energy indicator for machines whose main purpose is water cooling and air cooling, and SCOP is an energy indicator for heat pumps.

[0172] Practice has proved that the present invention has achieved the expected tasks and objectives.

[0173] In particular, the present invention develops a screw compressor that is able to perform the necessary and sufficient work required in the system in which the same screw compressor is inserted, without requiring additional energy consumption, and under a wider range of operating conditions.

[0174] Furthermore, the present invention develops a screw compressor capable of minimizing its own energy consumption.

[0175] The invention thus conceived is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept; moreover, all the details may be replaced by other technically equivalent elements.

[0176] In practice, the components and materials used, as long as they are compatible with the specific use, as well as the dimensions and possible shapes, may be any according to requirements and the state of the art.

[0177] If features and techniques mentioned in any of the claims are followed by reference numerals, these reference numerals are used only to increase the intelligibility of these claims and thus, these reference numerals have no limiting effect on the interpretation of each element identified by these reference numerals by way of example.

Claims

1. A screw compressor (10), in particular for use in a refrigeration circuit, comprising: - a containing body (11), the containing body (11) further comprising: - a suction chamber (11a) and a suction port (12) for the fluid to be compressed; - a delivery chamber (11b) and a discharge port (13) for said compressed fluid; - a housing seat (4) for two screw compression rotors (15, 16) placed side by side, the housing seat (14) being interposed between the suction chamber (11a) and the discharge chamber (11b), the housing seat (14) comprising an inlet opening (21) and an outlet opening (22) for the fluid; - two helical compression rotors (15, 16) placed side by side, each of said helical compression rotors (15, 16) having a helical protrusion configured to engage with a helical protrusion of the other compression rotor to define one or more compression chambers for said fluid; - an electric motor (17) for actuating the screw compression rotors (15, 16); - a lubricating device (18) having a lubricating fluid for the screw compression rotors (15, 16); - a filter device (19) for the compressed fluid, the filter device (19) being used to separate the lubricating fluid from the compressed fluid; - a frequency converter (23) connected to the electric motor (17); - an electronic control unit (24) configured to control and manage the frequency converter (23), It is characterized in that it also includes: - a low pressure sensor (25) positioned at the suction port (12) and connected to the electronic control unit (24); - a high pressure sensor (26) positioned at the discharge port (13) and connected to the electronic control unit (24); - an adjusting valve core (27), the adjusting valve core (27) being configured to adjust the width of the outlet opening (22); - a fluid actuating device (28), the fluid actuating device (28) being configured to move the regulating valve core (27), the fluid actuating device (28) being controlled by the electronic control unit (24); an ammeter (30) configured to measure the current absorbed by the electric motor (17) during operation of the compressor; The control unit (24) is configured as follows: - measuring the outlet pressure (Hp) by means of the high pressure sensor (26) and measuring the inlet pressure (Lp) by means of the low pressure sensor (25); - calculating the compression ratio (Pr) between the outlet pressure (Hp) and the inlet pressure (Lp); - measuring the current (Ivi) absorbed by the electric motor (17); - commanding the fluid actuating device (28) to move the regulating valve element (27) to a balance in which the current (Ivi) absorbed by the electric motor (17) is as low as possible according to the compression ratio (Pr); - Determine the optimal inherent volume ratio (Vi -最佳 ), i.e., the inherent volume ratio corresponding to the position of the regulating valve core (27), which determines the minimum absorption (Ivi-min) of the current absorbed by the electric motor (17); - regularly or continuously measuring the rotation speed (nr) of the electric motor (17), and regularly or continuously measuring the outlet pressure (Hp) and the inlet pressure (Lp) to regularly calculate the compression ratio (Pr); - commanding the fluid actuator (28) so that the fluid actuator (28) moves the regulating valve core (27) to automatically maintain the optimal inherent volume ratio (Vi -最佳 ).

2. The screw compressor according to claim 1, characterized in that: The fluid actuation device (28) includes an oil-operated actuator (34) having a rod (35) fixed to the regulating valve core (27).

3. The screw compressor according to the preceding claim, characterized in that The oil-powered actuator (34) comprises: - a piston (36) attached to the rod (35); - a first chamber (37) configured to receive pressurized oil to push the piston (36) in a first direction, thereby actuating the regulating valve core (27); A second chamber (38) in which a counter-thrust device is present, the counter-thrust device being configured to push the piston (36) in a second actuation direction of the regulating valve core (27) opposite to the first actuation direction.

4. Screw compressor according to the preceding claim, characterized in that The reverse thrust device is composed of a coil spring (39).

5. Screw compressor according to one or more of the preceding claims, characterized in that The fluid actuating device (28) comprises: - a pressurized oil loading line (40) configured as a passage for oil from the collecting tank (18a) to the first chamber (37); - a discharge line (41) configured as a passage for oil from the first chamber (37) to the suction chamber (11a); - a first one-way solenoid valve (42), the first one-way solenoid valve (42) being used to open the loading pipeline (40); - a second one-way solenoid valve (43) for opening the discharge line (41).

6. Screw compressor according to the preceding claim, characterized in that The first one-way solenoid valve (42) and the second one-way solenoid valve (43) are controlled by the electronic control unit (24).

7. The screw compressor according to claim 5, characterized in that: The loading line (40) and the discharge line (41) are connected at a bidirectional section (44), which is directly connected to the first chamber (37) of the oil-powered actuator (34).

8. Method for operating a screw compressor according to one or more of the preceding claims, characterized in that The method includes automatically searching for the optimal intrinsic volume ratio (Vi -最佳 ) and automatically controlling and maintaining the optimum inherent volume ratio (Vi -最佳 ) of the second step (200).

9. The method according to claim 8, characterized in that The first step (100) includes the following steps: - causing the electric motor (17) to reach a preset minimum speed (nr-min2); - Maintaining the minimum speed (nr-min2) for a period of time (T_nr-min2); -Start with the optimal inherent volume ratio (Vi -最佳 ) wherein upon activation, the piston (36) of the fluid actuating device (28) is in a starting position with a minimum outlet opening (22); -Measure output pressure (Hp) and input pressure (Lp), calculate (Pr) and store (Pr); - Simultaneously measuring the current (Ivi) absorbed by the electric motor (17) at the start of the search -起始 ) and stores the current value (Ivi -起始 ); -In the time interval (T -打开A ) enables the regulating valve core (27) to make a first movement so that it moves from the starting position with the minimum outlet opening (22) to the maximum outlet opening (22); - During the first movement of the regulating spool (27), the value of the absorbed current (Ivi) is measured and the minimum value of the absorbed current (Ivi) is stored -低 ); - measuring and storing the value of the absorbed current at the end of the movement of the regulating slide valve (27) (Ivi - ); -In the time interval (T -打开B ) to enable the regulating valve core (27) to move a second time so that it moves from the position reached by the first movement to a starting position with a minimum outlet opening (22); - During said second movement of said regulating valve core (27), the value of the absorbed current is measured (Ivi -最佳 ); -If Ivi -最佳 Basically equal to Ivi -低 , unless a variable (Delta-I) appears, that is, if There -低 -Delta-I<Ibid. -最佳 <There -低 +Delta-I Then for (Vi -最佳 )'s search is over; - Otherwise, we return to the initial step where the electric motor (17) is at a preset minimum speed (nr-min2).

10. The method according to claim 8 or 9, characterized in that: The second step (200) comprises (Vi -最佳 )'s second group automatically controls and maintains operation, (Vi -最佳 ) of the group of automatic control and maintenance operation comprises the following operating steps: - Check that the current rotation speed (nr) of the electric motor (17) is stable; - If the current speed (nr) is unstable, return to the initial step of checking the current speed (nr); -If the current speed (nr) is stable, then: - Check if the current compression ratio (Pr) is different from the previous value of said compression ratio (Pr -先前 ); - If the current compression ratio (Pr) is not different, return to the initial step of checking the current speed (nr); - If the current compression ratio (Pr) is different from the previous value (Pr -先前 ), search for the optimal inherent volume ratio (Vi -最佳 )'s new value; -Whether the measurement condition "Direction A" is applicable; - If "Direction A" is not applicable, save the current compression ratio (Pr) value as the previously stored compression ratio (Pr -先前 ) value, and moving the regulating valve core (27) toward the maximum opening position of the outlet opening (22); - If direction "A" applies, save the current compression ratio (Pr) value as the previously stored compression ratio (Pr -先前 ) value, and moving the regulating valve core (27) toward the minimum opening position of the outlet opening (22); - Check if the current being drawn (I) is lower than the previous value of the current being drawn (I -先前 ); - If the current currently absorbed (I) is lower than the previously stored value of the absorbed current (I -旧的 ), then reverse the moving direction of the regulating slide valve (27), and save / store the current value (I) currently absorbed as the previous current value (I -先前 ); - Check whether the current speed (nr) is stable; - If the current speed (nr) is unstable, return to the initial step of checking the current speed (nr); - If the current speed (nr) is stable, return to the condition "Direction A"; - The current absorbed (I) is not lower than the previous value of the absorbed current (I -先前 ),but: - Check if the current being drawn (I) is greater than the previous value of the drawn current (I -先前 ); - If the current absorbed (I) is greater than the previous value of the absorbed current (I -先前 ), the current absorbed current value (I) is saved as the previous absorbed current value (I -先前 ); - Check if the current speed (nr) is stable as described above; - If the current absorbed (I) is not greater than the previous current absorbed (I -先前 ), the current compression ratio (Pr) is saved as the previous compression ratio (Pr -先前 ) and return to the beginning.

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