REFRIGERANT COMPRESSOR

Abstract

In a refrigerant compressor for refrigeration plants, comprising a compressor unit driven by a drive unit, wherein at least one of these units is provided with a control unit which is controllable by means of a delivery rate control system in order to control the refrigerant compressor at different delivery rates, wherein an external delivery rate setpoint value is communicated to the delivery rate control system, in order to prevent critical operating states, it is proposed that the delivery rate control system acquires, by means of a sensor, a compressor reference temperature of the compressor unit, that the delivery rate control system ascertains an operating state value group for the acquisition of an operating state of the refrigerant compressor and, taking account of specified reference values, if the value of the ascertained operating state value group based upon the compressor reference temperature permits a critical operating state of the refrigerant compressor, specifies a delivery rate which has as its result an operation of the refrigerant compressor outside of the critical operating states.

Claims

1. A refrigerant compressor for refrigeration plants, comprising a compressor unit driven by a drive unit, wherein at least one of these units is provided with a control unit which is controllable by means of a delivery rate control system in order to control the refrigerant compressor at different delivery rates, wherein an external delivery rate setpoint value is communicated to the delivery rate control system, the delivery rate control system acquires, by means of a sensor, a compressor reference temperature of the compressor unit, in that the delivery rate control system ascertains an operating state value group for acquisition of an operating state of the refrigerant compressor on the basis at least of the acquired compressor reference temperature or the delivery rate and, taking account of specified reference values for differentiating between operating states that are non-critical and critical for the refrigerant compressor, if the value of the ascertained operating state value group based upon the compressor reference temperature permits a critical operating state of the refrigerant compressor, specifies a delivery rate which has as its result an operation of the refrigerant compressor outside of the critical operating states.

2. The refrigerant compressor according to claim 1, wherein the delivery rate control system ascertains the operating state value group based upon the acquired compressor reference temperature and the delivery rate.

3. The refrigerant compressor according to claim 1, wherein when ascertaining the values of the operating state value group of the refrigerant compressor, the delivery rate control system ascertains a mean value of the delivery rate over a defined acquisition period.

4. The refrigerant compressor according to claim 3, wherein the defined acquisition period is in the range from one minute to 30 minutes.

5. The refrigerant compressor according to claim 1, wherein when ascertaining the values of the operating state value group, the delivery rate control system ascertains a mean value of the compressor reference temperature over a defined acquisition period.

6. The refrigerant compressor according to claim 5, wherein the defined acquisition period is in the range from 30 seconds to 15 minutes.

7. The refrigerant compressor according to claim 1, wherein the delivery rate control system takes into account as the compressor reference temperature at least one of the temperatures such as the compressed gas temperature on the high pressure side of the compressor unit, the oil temperature of the compressor unit and the temperature of the drive unit.

8. The refrigerant compressor according to claim 1, wherein, for ascertaining the values of the operating state value group, the delivery rate control system acquires the delivery rate based upon control signals for at least one of the units.

9. The refrigerant compressor according to claim 1, wherein, during the determination of the delivery rate to be specified, the delivery rate control system takes account of the value, based upon the acquired delivery rate, of the operating state value group in relation to the reference values.

10. The refrigerant compressor according to claim 9, wherein the delivery rate control system compares the value, based upon the acquired delivery rate, of the operating state value group with the reference values.

11. The refrigerant compressor according to claim 1, wherein, for the ascertainment of the delivery rate to be specified, the delivery rate control system uses at least one value for the delivery rate that is specified by means of the reference values, said value lying outside of the critical operating states.

12. The refrigerant compressor according to claim 1, wherein the delivery rate control system specifies the delivery rate such that an averaging of the delivery rate over an operating averaging period yields a total delivery rate that lies outside of the critical operating states.

13. The refrigerant compressor according to claim 1, wherein the reference values comprise at least one limit value for the delivery rate which defines a limit to the critical operating states.

14. The refrigerant compressor according to claim 1, wherein a limit function representing the reference values which defines the boundary between the non-critical and critical operating states is specified to the delivery rate control system.

15. The refrigerant compressor according to claim 1, wherein the delivery rate control system specifies the delivery rate such that it corresponds to at least the respective value of the limit function at the value of the operating state value group based upon the compressor reference temperature.

16. The refrigerant compressor according to claim 1, wherein the delivery rate control system specifies the delivery rate such that an averaging of the delivery rate over an operating averaging period achieves at least the respective value of the limit function.

17. The refrigerant compressor according to claim 1, wherein the operating averaging period comprises the acquisition period for the value of the operating state value group based upon the delivery rate.

18. The refrigerant compressor according to claim 14, wherein the operating averaging period is greater than the acquisition period for the value of the operating state value group based upon the delivery rate.

19. The refrigerant compressor according to claim 16, wherein the operating averaging period also comprises a future period.

20. The refrigerant compressor according to claim 1, wherein for ascertaining the delivery rate, the delivery rate control system generates an internal delivery rate setpoint value and takes account thereof for the determination of the delivery rate.

21. The refrigerant compressor according to claim 20, wherein the delivery rate control system makes use, as the internal delivery rate setpoint value, of at least the value for the delivery rate corresponding to the value based upon the compressor reference temperature and specified by the limit function.

22. The refrigerant compressor according to claim 20, wherein the delivery rate control system ascertains the internal delivery rate setpoint value taking account of an averaging over future delivery rates corresponding to this internal delivery rate setpoint value within the operating averaging period.

23. The refrigerant compressor according to claim 20, wherein the internal delivery rate setpoint value is determined such that the future delivery rates corresponding thereto in conjunction with the value of the operating state value group based upon the delivery rate yields a mean total delivery rate which corresponds to the limit value, specified at the mean compressor reference temperature by the limit function, for the total delivery rate.

24. The refrigerant compressor according to claim 23, wherein the future delivery rates corresponding to the internal delivery rate setpoint value are averaged over a future acquisition period.

25. The refrigerant compressor according to claim 16, wherein the operating averaging period is composed of the past acquisition period for the value of the operating state value group based upon the delivery rate and the future acquisition period for averaging the future delivery rates.

26. The refrigerant compressor according to claim 1, wherein for the specification of the delivery rate, the delivery rate control system takes account of the internally ascertained delivery rate setpoint value for as long as the externally specified delivery rate setpoint value lies below the internally ascertained delivery rate setpoint value.

27. The refrigerant compressor according to claim 1, wherein the delivery rate control system compares the internally ascertained delivery rate setpoint value and the externally specified delivery rate setpoint value with one another and takes the larger of the delivery rate setpoint values into account for controlling the delivery rate.

28. The refrigerant compressor according to claim 1, wherein the delivery rate control system generates a signal if the refrigerant compressor is operated with an internally ascertained delivery rate setpoint value.

29. The refrigerant compressor according to claim 1, wherein the delivery rate control system generates an information signal if the delivery rate is determined by the external delivery rate setpoint value.

30. The refrigerant compressor according to claim 1, wherein an advance warning range in which non-critical operating states exist which adjoin the specified limit function is specified to the delivery rate control system.

31. The refrigerant compressor according to claim 1, wherein the delivery rate control system generates an advance warning signal if operating state value groups that lie within the advance warning range are recognized.

32. The refrigerant compressor according to claim 1, wherein the delivery rate control system drives a fan and/or a refrigerant injection device for cooling the refrigerant compressor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0095] FIG. 1 is a schematic representation of a refrigeration plant according to the invention;

[0096] FIG. 2 is a transverse section along the line 2-2 through a refrigerant compressor of the refrigeration plant according to the invention;

[0097] FIG. 3 is a section through a mechanical delivery rate control unit integrated into a cylinder head in the opened position of a valve body of the mechanical delivery rate control unit;

[0098] FIG. 4 is a section similar to FIG. 3 in a closed position of the valve body of the mechanical delivery rate control unit;

[0099] FIG. 5 is a schematic representation of a switching interval comprising an opening interval and a closing interval;

[0100] FIG. 6 is a schematic representation of an operating diagram;

[0101] FIG. 7 is a flow diagram of a first exemplary embodiment to illustrate the procedure according to the invention;

[0102] FIG. 8 is a representation of reference values specified by means of a limit function in the first exemplary embodiment for differentiating between non-critical and critical operating states;

[0103] FIG. 9 is a flow diagram similar to FIG. 7 of a second exemplary embodiment;

[0104] FIG. 10 is a representation similar to FIG. 8 of reference values specified by means of a limit function in the second exemplary embodiment;

[0105] FIG. 11 is a flow diagram similar to FIG. 9 of a third exemplary embodiment;

[0106] FIG. 12 is a portion of a flow diagram of a fourth exemplary embodiment;

[0107] FIG. 13 is a schematic representation of the refrigeration plant similar to FIG. 1 comprising the variant according to the fourth and fifth embodiments, and

[0108] FIG. 14 is a portion of a flow diagram according to a fifth exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0109] An exemplary embodiment of the refrigeration plant according to the invention comprises a refrigerant compressor 10 from the high pressure connector 14 of which, a line 16 leads to a heat exchanger identified overall as 18 in which the compressed refrigerant is condensed through the removal of heat to a heat sink, for example, circulated ambient air or other cooling media.

[0110] From the high pressure-side heat exchanger 18, liquid refrigerant flows in a line 20 to a collector 22 in which the liquid refrigerant collects and from which it then flows via a line 28 to an expansion element 30 for a low pressure-side heat exchanger 32 and absorbs heat, for example, from a gaseous medium flowing therethrough.

[0111] After flowing through the low pressure-side heat exchanger 32, the evaporated refrigerant flows via a line 34 to a low pressure connector 36 of the refrigerant compressor 10.

[0112] As FIG. 2 shows, the refrigerant compressor 10 according to the invention has, for example, a reciprocating piston compressor as the compressor unit 40, comprising a compressor housing 38 in which, for example, two cylinder banks 42a and 42b are provided, operating in parallel and arranged in a V-shape, each of said banks comprising at least one, in particular, two or more cylinder units 44.

[0113] Each of these cylinder units 44 is formed from a cylinder housing 46 in which a piston 48 is movable reciprocatingly in that the piston 48 is drivable by means of a connecting rod 50 which itself is attached to an eccentric 52 of an eccentric shaft 54 or is driven by a crankshaft which is driven, in the refrigerant compressor 12 according to the invention, by a drive unit 60 configured as an electric motor, wherein the electric motor can be configured as a synchronous or an asynchronous motor.

[0114] The cylinder housing 46 of each of the cylinder units 44 is closed by a valve plate 56 on which a cylinder head 58 is arranged.

[0115] Preferably, the valve plate 56 covers not only a cylinder housing 46 of a cylinder unit 44, but all the cylinder housings 46 of the respective cylinder bank 42 and, in the same way, the cylinder head 58 also extends over the cylinder head 58 of all the cylinder housings 46 of the respective cylinder bank 42.

[0116] The compressor housing 38 further comprises an inlet channel 62 which is connected to the low pressure connector 36 and is integrated, for example, in the compressor housing 40.

[0117] As shown enlarged in FIG. 3, associated with at least one cylinder bank 42, in the drawing each cylinder bank 42, is a mechanical control unit identified as a whole as 70, which serves to admit an inlet stream 74 of refrigerant passing through the valve plate 56 from the inlet channel 62 into the respective cylinder head 58, specifically into an inlet chamber 72 thereof in order thus to activate the respective cylinder bank 42, or to interrupt said inlet stream in order thus to deactivate the respective cylinder bank 42 and to control the delivery rate FV that is to be specified.

[0118] If the mechanical control unit 70 is opened—as shown in FIG. 3—the inlet stream 74 has the possibility to enter via an inlet opening 76 provided in the valve plate 56 and an inlet valve 78 provided on the valve plate 56 into a cylinder chamber 80 delimited by the respective piston 48 and the respective cylinder housing 46 as well as the valve plate 56, in order to be compressed therein by the reciprocating movement of the piston 48, so that an outlet stream 86 emerges from the cylinder chamber 80 via an outlet opening 82 and an outlet valve 84 and enters into an outlet chamber 88 of the cylinder head 58.

[0119] The mechanical control unit 70 is configured, for example, as a servo valve which is integrated in the cylinder head 58 and has a valve body 90 with which an inflow opening 92 of the inlet chamber 72 provided in the valve plate 56 is closable.

[0120] The valve body 90 is further arranged on a switching piston 94 which is guided in a switching cylinder housing 96 so that the switching piston 94 is movable in the direction of the valve plate 56 by a pressure present in a switching cylinder chamber 98 in order to close the inflow opening 92 therein.

[0121] A switching cylinder unit 100, formed from the cylinder housing 96, the switching piston 94 and the switching cylinder chamber 98, which is integrated into the cylinder head 58 is controllable therein by means of a control valve 110 which comprises an electromagnetically movable control piston 112 with which a control valve seating 114 is closable, wherein the control piston 112 and the control valve seat 114 are provided to interrupt or uncover a connection between a high pressure channel 116 leading to the outlet chamber 88 and a pressure feed channel 118 for the switching cylinder 100.

[0122] If the connection between the high pressure channel 116 and the pressure feed channel 118 is uncovered, the switching cylinder chamber 98 is exposed to the high pressure prevailing in the outlet chamber 88 and consequently the switching piston 94 moves in the direction of the valve plate 56 and presses the valve body 90 thereagainst in order to close the inflow opening 92 in the valve plate 56 (FIG. 4).

[0123] Thereby, the force acting on the switching piston 94 due to the high pressure in the switching cylinder chamber 98 counteracts the force of an elastic energy store 120 which, on one side, is supported against the switching cylinder housing 96 and, on the other side, acts upon the switching piston 94 such that said switching piston moves away from the valve plate 56 and thus moves the valve body 90 into a position uncovering the inflow opening 92.

[0124] In particular, the switching piston 94 is provided with a pressure relief channel 122 which extends from an opening facing the switching cylinder chamber 98 to an outlet opening 124 shown in FIG. 4, said outlet opening, in the position of the valve body 90 and the switching piston 94 closing the inflow opening 92, opening into the inlet chamber 72. The pressure relief channel 124 has the effect thereby that, on an interruption of the connection between the high pressure channel 116 and the pressure feed channel 118, the pressure in the switching cylinder chamber 98 rapidly collapses and thus the switching piston 94 together with the valve body 90 move under the effect of the elastic energy store 120 into a position shown in FIG. 3, uncovering the inflow opening 92.

[0125] The mechanical control unit 70 is controllable by a delivery rate control system 130 shown in FIG. 1 by means of control signals SSM, whereby the mechanical control unit 70 can be closed or opened in order to activate or deactivate the respective cylinder bank 42a, 42b and thus to put the refrigerant compressor 12 into an operating mode defining the scope of the activation and deactivation of the cylinder banks 42.

[0126] In addition, with the delivery rate control system 130, the drive motor 60 is also controllable via control signals SSE by means of a control unit 140 which is configured, in particular, as a frequency converter for the electric motor 60 in order to be able to operate it at variable rotary speed and thereby also, alternatively or in addition to the mechanical control units 70, to be able to control the delivery rate FV that is to be specified.

[0127] Furthermore, the delivery rate control system 130 has the possibility of acquiring the respective delivery rate FV of the refrigerant compressor 10, for example, by means of the control signals SSM.

[0128] Additionally, the delivery rate FV to be specified can be acquired, insofar as it is influenced by the frequency converter 140, by means of the electrical power consumed by the electric motor 60 or by the control signals SSE.

[0129] In addition, an external delivery rate setpoint value EFVS which is generated by a plant control system 138 is also specified to the delivery rate control system 130, said plant control system acquiring the cooling power required at the low pressure-side heat exchanger 32 for cooling an object 146, for example, a cooling chamber, for example, by means of temperature sensors 142 and 144 associated with the low pressure-side heat exchanger 32, which enable it to acquire the temperatures of a medium 148 flowing through the low pressure-side heat exchanger 32 and the object 146, for example, before and after the low pressure-side heat exchanger 32, and to compare them with a required temperature of the medium 146.

[0130] In one control step, through the generation of suitable control signals SSM and SSE, the delivery rate control system 130 adapts the cooling power of the refrigeration plant 10 to the cooling power required for the cooling of the object 146 through the selection of a suitable operation of the compressor unit 10 by means of the control unit 70 and/or by means of a possible regulation of the rotary speed of the electric motor 60 by means of the frequency converter 140, wherein as the basis for this adaptation, the external delivery rate setpoint value EFVS generated by the plant control system 138 is utilized.

[0131] In particular, however, for the adaptation of the rotary speed, due to the construction of the electric motor 60, only a restricted rotary speed range is available, which is also to be taken into account in the selection of the suitable operation.

[0132] The operation possible in partial load states can provide, for example,

[0133] an operation of the refrigerant compressor 10 with all the cylinder banks 42 in the active state with or without an adaptation to the partial load state by adaptation of the rotary speed of the electric motor 12 by the frequency converter 132,

[0134] an operation of the refrigerant compressor 10 with active and inactive cylinder banks 42, with or without an adaptation of the rotary speed of the electric motor 12 by the frequency converter 132 to the capacity of the active and inactive cylinder banks, an operation of the refrigerant compressor 10 with just one active cylinder bank 42 and an adaptation to the partial load state by adaptation of the rotary speed of the electric motor 12 by the frequency converter.

[0135] The activation or deactivation of at least one of the cylinder banks 42a, 42b can take place, for example, in a first mode of operation, over the entire period of the respective partial load state, so that for example, during a particular period in which a partial load state of X % of the full load state is required, one cylinder bank 42 is constantly deactivated and the refrigerant compressor 12 functions with the respective other active cylinder bank 42, and possibly also a corresponding adaptation of the rotary speed of the electric motor takes place through corresponding control of the frequency converter 132.

[0136] Alternatively thereto, however, it is also possible in a second type of operation to activate or deactivate at least one cylinder bank 42a, 42b or both cylinder banks 42 in a clocked manner during the period of a partial load state and/or possibly also to adapt the rotary speed of the electric motor 60 in a suitable manner by controlling the frequency converter 132.

[0137] For this purpose, the mechanical control unit 70 is controllable by the delivery rate control system 130 shown in FIG. 1 such that thereby in continuously successive switching intervals SI, the mechanical control unit 70 closes and opens, whereby each of the switching intervals SI has an opening interval O in which the valve body 90 in its uncovering position permits a passage of the inlet stream 74 through the inflow opening 92 and activates the corresponding cylinder bank 42, and also has a closing interval S in which the valve body 90, as shown in FIG. 4, in its closing position blocks the passage of the inlet stream 74 through the inflow opening 92 and thus deactivates the corresponding cylinder bank 42.

[0138] Within the duration of the respective switching interval SI, the duration of the opening interval O and of the closing interval S relative to one another can be variably set so that either the opening interval O is greater than the closing interval or vice versa.

[0139] In an extreme case, the opening interval O can extend substantially over the whole duration of the switching interval SI, whereas the closing interval S becomes as small as desired or, conversely, the closing interval S can extend substantially over the entire duration of the switching interval SI, so that the opening interval O becomes as small as desired.

[0140] The delivery rate control system 130 according to the invention operates the refrigerant compressor 10, in principle, within the operating diagram ED, shown in FIG. 6, which illustrates an example of an operating diagram ED for a compressor and which indicates the relationship of the values of the suction pressure PS and the high pressure PH permissible for a specific refrigerant compressor 10, wherein in the control step identified in FIG. 7 with 162, the control signals SSM and/or SSE are generated based upon one of two delivery rate setpoint values, specifically the external delivery rate setpoint value EFVS and an internal delivery rate setpoint value IFVS to be described in greater detail below.

[0141] However, the operating diagram ED does not take into account that, in particular, with a reduced delivery rate FV in the operating diagram ED, an overheating can occur, for example, in the regions UEB1 of the operating diagram ED, shown shaded in FIG. 6, since at a reduced delivery rate FV over a relatively long period, due to the reduced throughflow of the medium to be compressed, said medium also having a cooling function, an inadmissible heating occurs in the compressor unit 40, so that an overheating not only of the compressor unit 40, but also of the entire refrigerant compressor 10 can occur, leading to damage, although the refrigerant compressor 10 is operated within the limits specified by the operating diagram ED.

[0142] For this reason, in the solution according to the invention, an acquisition of a compressor reference temperature RT by the delivery rate control system 130 takes place by means of a sensor 152, in particular a temperature sensor which is arranged, for example, in the region of the high pressure connector 14.

[0143] However, alternatively or additionally, an oil temperature of the compressor unit (40), acquired by means of a sensor 152′ and/or a temperature of the drive unit acquired by means of a sensor 152″ can be used as the compressor reference temperature RT.

[0144] Furthermore, in an acquisition step 164, the delivery rate control system 130 acquires the delivery rate FV of the refrigerant compressor 10, for example, by acquisition of the generated control signals SSM and/or SSE, wherein the delivery rate FV corresponds, for example, without additional measures, as described below, of the delivery rate control system 130, to one of the delivery rate setpoint values IFVS or EFVS.

[0145] If, for example, the refrigerant compressor 10 runs at a reduced delivery rate FV in a partial region, the delivery rate control system 130 acquires the operating state of the refrigerant compressor 10 by forming an operating state value group BZW on the basis, for example, of the compressor reference temperature RT and the delivery rate FV, and, in a comparison step 166, compares this operating state value group BZW with reference values GF stored, for example, in a memory store 154 of the delivery rate control system 130 in order to recognize possibly occurring critical operating states KB (FIG. 8).

[0146] In particular, the formation of the momentary values of the operating state value group BZW in that it is not a simple acquisition of the compressor reference temperature RT or the momentary delivery rate FV that takes place, but rather, in a mean value step 168 arranged before the comparison step 166, the delivery rate control system 130 ascertains a mean value MFV of the delivery rate FV over a defined acquisition period t.sub.1, wherein the defined acquisition period t.sub.1 is preferably a plurality of minutes, for example, within a range from one minute to 30 minutes (FIG. 7), and a mean value MRT over a defined acquisition period, preferably a plurality of minutes, wherein the acquisition period lies, in particular, within a range from 30 seconds to 15 minutes (FIG. 7).

[0147] This operating state value group BZW comprising the mean values MFV and MRT is compared in the comparison step 166 by the delivery rate control system 130 with reference values GF stored in the memory store 154 for critical KB and non-critical UB operating states (FIG. 8).

[0148] The reference values for non-critical UB and critical KB operating states defines, for example, a first version of a limit function GF stored in the memory store 154, which is relevant from a minimum mean compressor reference temperature MRT.sub.min, since below the minimum mean compressor reference temperature MRT.sub.min there exist non-critical operating states in any event (FIG. 8).

[0149] In addition, the limit function GF is relevant, for example, from a minimum total delivery rate GFVF.sub.min provided the mean compressor reference temperature MRT is higher than MRT.sub.min.

[0150] The limit function GF has been stipulated in this case so that, for example, at mean compressor reference temperatures MRT that are higher than the mean compressor reference temperature MRT.sub.min, with increasing mean compressor reference temperature MRT, it requires increasingly larger mean total delivery rates GFV, wherein in the simplest case, the limit function GF represents a straight line with a specified slope.

[0151] The limit function GF can however also be a curved line, depending on which mean compressor reference temperatures MRT and which total delivery rates GFV lie in a critical or non-critical region UB.

[0152] For example, in a refrigerant compressor 10, the minimum mean compressor reference temperature MRT.sub.min is 120°, which means that up to the mean compressor reference temperature MRT.sub.min, the refrigerant compressor 10 can be operated damage-free at the total delivery rate GFV.sub.min and any higher total delivery rate GFV (FIG. 8).

[0153] The limit function GF thus represents a boundary between the critical KB and non-critical UB operating states if the operating state value groups BZW have a value MRT based upon a compressor reference temperature RT that is higher than MRT.sub.min, wherein the values of the total delivery rate GFV at critical operating states KB below or at non-critical operating states UB, lie above the values defined by the limit function GF.

[0154] If the delivery rate control system 130 determines in an evaluating step 172 that the operating state value group BZW has a value MRT, based upon the compressor reference temperature RT, which lies above the minimum mean compressor reference temperature MRT.sub.min, in a first exemplary embodiment, in a setpoint value step 174, an ascertainment takes place of an internal delivery rate setpoint value IFVS which results from the following calculation, starting from the limit function GF, which has been determined such that it assigns as reference values, values of a total delivery rate GFV corresponding to different mean compressor reference temperatures MRT.

[0155] It is assumed that the value of the total delivery rate GFV corresponding to the mean compressor reference temperature MRT should be at least maintained.

[0156] Thereby, the value GFV is to correspond to a total delivery rate GFV that is achieved by averaging the delivery rate FV during an operating averaging period t.sub.1+t.sub.2, said period resulting firstly from the past acquisition period t.sub.1 over which the delivery rate FV has been averaged during the calculation of the mean delivery rate MFV, and secondly from a future acquisition period t.sub.2 over which an averaging of the future internal delivery rate setpoint value IFVS that is to be set is to take place, so that

GFV×(t.sub.1+t.sub.2)=MFV×t.sub.1+IFVS×t.sub.2

[0157] Thus, for the delivery rate setpoint value that is to be ascertained

[00001]$\mathrm{IFVS}=\frac{\mathrm{GFV}\times \left(t_1+t_2\right)-\mathrm{MFV}\times t_1}{t_2}$

[0158] This internal delivery rate setpoint value IFVS is transferred to a comparison step 176 in FIG. 7 which compares the internal delivery rate setpoint value IFVS with the external delivery rate setpoint value EFVS and then, if the external delivery rate setpoint value EFVS is smaller than the internal delivery rate setpoint value IFVS, transfers the latter to the control step 162 and then, if the internal delivery rate setpoint value IFVS is smaller than the external delivery rate setpoint value EFVS, transfers the latter to the control step 162.

[0159] It is thereby ensured that the total delivery rate GFV averaged over the operating averaging period t.sub.1+t.sub.2 does not undershoot the value for the total delivery rate specified by the limit function GF and thus on average, this value is not undershot at the mean compressor reference temperature MRT.

[0160] In a second exemplary embodiment, if the delivery rate control system 130 determines in the evaluating step 172 that the operating state value group BZW comprising the mean delivery rate MFV and the mean compressor reference temperature MRT has value pairings which (according to FIG. 10) have a mean compressor reference temperature MRT in the region of the limit function GF, that is, above the mean compressor reference temperature MRT.sub.min and a mean delivery rate MFV that lies above the corresponding value GF.sub.MDT of the limit function GF, the delivery rate control system 130 determines a non-critical operating state UB and a continuation of the operation with the externally specified delivery rate setpoint value EFVS (FIG. 9) and a renewed passage through the steps 162 to 168 takes place.

[0161] If, however, the mean compressor reference temperature MRT at the operating state value group BZW lies above the mean compressor reference temperature MDT.sub.min and the mean delivery rate MFV lies below the value MFV(GF) of the limit function GF corresponding to the compressor reference temperature MRT for the mean delivery rate MFV, then the delivery rate control system 130 detects a critical operating state KB in the setpoint value step 174 (FIG. 10).

[0162] The delivery rate control system 130 then ascertains in the setpoint value step 174, taking account of the limit function GF, an internal delivery rate setpoint value IFVS which corresponds to a mean delivery rate MFV (GF), which is specified by or lies above the limit function GF, so that a continuation of the operation of the refrigerant compressor 10 in the non-critical operating state UB or corresponding to the limit defined by the limit function GF between the non-critical operating state UB and the critical operating state KB takes place (FIG. 9).

[0163] Thus, in the second exemplary embodiment, the operating averaging period represents just the period t.sub.1 that is used for the determination of the mean delivery rate MFV (GF).

[0164] This internal delivery rate setpoint value IFVS is then fed to the comparison step 176 of the delivery rate control system 130 shown in FIG. 9, which compares the internal delivery rate setpoint value IFVS with the external delivery rate setpoint value EFVS and feeds the larger value of the two to a control step 162 for controlling the delivery rate MFV of the refrigerant compressor 10, in particular, for controlling the mechanical control unit 70 by means of the control signals SSM and/or the electrical control unit 140 by means of the control signals SSE, so that thereby, a continuation of the operation of the refrigerant compressor 10 can take place without damage occurring.

[0165] A third exemplary embodiment, shown in FIG. 11, which is based upon the second exemplary embodiment, provides that the delivery rate control system 130 does not acquire the actual delivery rate FV, but only checks in the evaluating step 172 whether the operating state value group BZW has a value MRT based upon the compressor reference temperature RT which lies above the minimum compressor reference temperature MRT.sub.min and then if this is the case, without a comparison of the value of the operating state value group BZW on the basis of the delivery rate FV with the value MFV(GF) specified by the limit function GF for this compressor reference temperature MRT, uses the value MFV (GF) directly as the internal delivery rate setpoint value IFVS.

[0166] In all the exemplary embodiments, the delivery rate control system 130 always continues to operate with the internal delivery rate setpoint value IFVS if an external delivery rate setpoint value EFVS which is smaller than the internal delivery rate setpoint value IFVS is specified by the plant control system 138, so that thereby it is necessarily ensured that the refrigerant compressor 10 is operated with a mean total delivery rate GFV(GF) or delivery rate MFV(GF) which is larger at the existing mean compressor reference temperature MRT than the mean total delivery rate GFV(GF) or the mean delivery rate MFV(GF) required by the limit function GF or corresponds thereto, so that thereby an overheating of the refrigerant compressor 10 can be prevented (FIG. 10).

[0167] In all the exemplary embodiments, only if an external delivery rate setpoint value EFVS that is larger than the internal delivery rate setpoint value IFVS is specified by the plant control system 138, it is fed by the comparison step 176 to the control step 162 and used for controlling the delivery rate FV of the refrigerant compressor 10.

[0168] Such an external delivery rate setpoint value EFVS, if it is larger than the internal delivery rate setpoint value IFVS, will lead to the compressor reference temperature RT and thus also the mean compressor reference temperature MRT being further reduced during operation so that also thereafter an operation of the refrigerant compressor 10 with an operating state value group BZW at which the mean delivery rate MFV has smaller values is possible.

[0169] Due to the comparison step 176 provided and in cooperation with the control step 162, it is ensured that the delivery rate FV is always controlled on the basis of the largest of the two delivery rate setpoint values IFVS and EFVS, so that a long lasting overheating of the refrigerant compressor 10 can be prevented.

[0170] In order to convey to the plant control system 138 or the plant operator that the refrigerant compressor 10 is controlled on the basis of the internal delivery rate setpoint value IFVS, since the external delivery rate setpoint value EFVS is smaller, in a fourth exemplary embodiment which represents a variant of the above exemplary embodiments, in the event that the internal delivery rate setpoint value IFVS is larger than the external delivery rate setpoint value EFVS, the comparison step 176 issues a warning signal WS which is output, for example, optically (FIG. 12 and FIG. 13).

[0171] Furthermore, the comparison step 176 issues an information signal IS which indicates that the external delivery rate setpoint value EFVS is larger than the internal delivery rate setpoint value IFVS so that thereby the plant operator or the plant control system 138 can recognize that the refrigerant compressor 10 is being operated with the external delivery rate setpoint value EFVS (FIG. 13).

[0172] In addition, in a fifth exemplary embodiment which represents a further variant of the exemplary embodiments of the delivery rate control system 130 according to the invention, it is further provided that, as shown in FIG. 14, the operating state value group BZW generated in step 166 is fed to a comparison step 192 which compares the operating state value group BZW with values of an advance warning function VWF stored in the memory store 154, said advance warning function extending in the region of non-critical operating states, but close to the limit function GF so that at the respective mean compressor reference temperature MRT, when it is higher than the mean compressor reference temperature MRT.sub.min mean delivery rates MFV which lie in the region between the advance warning function VWF and the limit function GF are recognized.

[0173] By means of the comparison step 192, in this case, an advance warning signal VWS is generated and output which indicates either to the plant user or the plant control system 138 (FIG. 13) that there is an appreciable probability that the refrigerant compressor 10 can enter the critical region.

[0174] For example, the plant control system 138 can independently use this advance warning signal VWS to increase the delivery rate FV by raising the external delivery rate setpoint value EFVS.

[0175] In particular, the possibility thus exists, with the warning signal WS, the advance warning signal VWS and the information signal IS, of operating a display unit 200 (FIG. 13) which either represents just the warning signal WS, the advance warning signal VWS and the information signal IS through the display of different colors or the display unit 200 can be configured as a screen which, for example, enables the symbols or graphics associated with the warning signal WS, the advance warning signal VWS and the information signal IS to appear.

[0176] In addition or alternatively, for this purpose it is however also provided that in the event of partial load states of the refrigerant compressor 10 or at least at low partial load states or by acquiring the operating states, for example, triggered by the advance warning signal VWS, the delivery rate control system 130 uses a fan 202 for cooling the compressor unit 40 and/or an injection 204 (FIG. 13) for suction-side injection of liquid coolant, in order to prevent critical operating states KB.