EP3405673B1 - Method for detecting a blocked valve of a coolant compressor and a control system for a coolant compressor - Google Patents

Description

FIELD OF THE INVENTION

The present invention relates to a method for detecting a blocked valve of a refrigerant compressor having a drive unit and a piston-cylinder unit for cyclically compressing a refrigerant, wherein the drive unit comprises an electric motor for driving the piston-cylinder unit, wherein the rotational speed of the electric motor monitors becomes.

Furthermore, the present invention relates to a control system for a refrigerant compressor, the refrigerant compressor comprising a drive unit and a piston-cylinder unit for cyclically compressing a refrigerant, wherein the drive unit comprises an electric motor for driving the piston-cylinder unit and wherein the control system comprises control electronics ,

STATE OF THE ART

In a refrigerant compressor having a drive unit and a piston-cylinder unit for cyclically compressing a refrigerant, wherein the drive unit comprises an electric motor for driving the piston-cylinder unit and wherein the Speed of the electric motor is controlled, there is a possible error condition in a blocked valve. This may in particular be a blocked suction or pressure valve. In practice, however, eg a solenoid valve in the cooling circuit may be defective, which solenoid valve does not necessarily have to be part of the refrigerant compressor.

The blocked valve in any case has the consequence that refrigerant in the cooling circuit is no longer transported in the extent required for cooling or not at all and therefore cooling can no longer take place. The application device driving the refrigerant compressor, e.g. a refrigerator, determines that the temperature does not drop, and then usually regulates the refrigerant compressor to maximum cooling capacity, so that the electric motor runs at maximum speed - of course, without success, because the coolant in the cooling circuit can not be transported.

Even if originally the cause of the blockage of the cooling circuit was not a blocked valve of the refrigerant compressor, the valve, in particular the pressure valve of the refrigerant compressor, is blocked at the latest now. This is because, due to the further operation of the compressor at the highest power level of the back pressure of the refrigerant in the pressure section increases so far that the pressure valve does not open, because the pressure built up by the refrigerant compressor is no longer sufficient for this. In general, there is always at least a blockage of the pressure valve when the back pressure is high enough - regardless of how this back pressure is achieved or generated.

To prevent the refrigerant compressor from continuing to run at high speed due to the fault condition It is known from the prior art, the increase in the temperature of the compressor, for example, over a certain limit temperature to define as a termination condition. That is, the temperature is constantly monitored, and when the limit temperature is exceeded and the electric motor preferably runs at maximum speed, the electric motor is turned off.

A disadvantage of this known method is that it does not work for all refrigerant compressors. The practice shows that depending on the design or type of refrigerant compressor, the temperature sometimes does not rise far enough to be able to determine a limit temperature meaningful.

For example, is from the JP 2003254587 A the detection of a blocked valve by detecting the rise in temperature on the pressure side of the compressor known.

OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide a method that enables the reliable detection of a blockage condition or a blocked valve of the compressor. Accordingly, it is a further object of the invention to provide a control system for a refrigerant compressor which enables reliable detection of a blockage condition of a compressor, in order to be able to set countermeasures.

PRESENTATION OF THE INVENTION

Elaborate test series with different types of refrigerant compressors, each having a drive unit and a piston-cylinder unit for cyclically compressing a refrigerant, wherein the drive unit comprises an electric motor for driving the piston-cylinder unit and wherein the rotational speed of the electric motor is monitored, have shown that the drastically reduced or even completely halting mass flow, which occurs in a blockage or a blocked valve, may cause that some monitoring parameters, although initially increase in value and reach a maximum value, but then decrease again within a certain, preferably predeterminable period of time, while the electric motor continues to run at maximum speed.

Here and below, "maximum speed" is always to be understood as the maximum speed that the refrigerant compressor or the electric motor actually achieves in the current cooling circuit. This maximum speed may differ for different reasons from a theoretically technically possible maximum speed of the electric motor, for example, because of noise reasons, the application ^device does not exploit or request the theoretically technically possible maximum speed of eg 4000 min ^-1 , but as a "target maximum speed" one lower speed of eg 3600 min ^-1 predetermines. Furthermore, a variety of external circumstances, such as a too low supply voltage, cause the target maximum speed (and of course the theoretically technically possible maximum speed of the electric motor) is not reached, so that the maximum speed actually lower than the target maximum speed (and Of course, as the theoretically technically possible maximum speed of the electric motor) is.

A typical monitoring parameter would be the current consumption of the electric motor, which after rising to a maximum, for example, 0.85 A, within a certain period of time to a certain value - for example, to 0.425 A - goes back, while the electric motor is constantly running at maximum speed.

As a decisive criterion for the presence of a blocked valve can therefore be used that the decrease of the monitoring parameter within the certain period of time is "large enough", this size depends on the particular type of refrigerant compressor and can be determined by a laboratory experiment and then specified accordingly.

• Bestimmung eines Maximalwerts X_max eines Überwachungsparameters des Kältemittelkompressors;
• Bestimmung eines Werts X_t1 des Überwachungsparameters nach einer ersten Zeitspanne nach der Bestimmung des Maximalwerts X_max;
• Detektion eines blockierten Ventils, wenn X_t1 kleiner als X_max ist und (X_max - X_t1)/ X_max ≥ Δ_X gilt, wobei Δ_X vorgegeben ist.

Accordingly, in a method of detecting a blocked valve of a refrigerant compressor having a drive unit and a piston-cylinder unit for cyclically compressing a refrigerant, the drive unit includes an electric motor for driving the piston-cylinder unit, wherein the rotational speed of the electric motor is monitored is inventively provided that first a maximum speed of the electric motor is detected and that the following steps are carried out as long as the speed of the electric motor substantially corresponds to the maximum speed:

• Determining a maximum value X _{max of} a monitoring parameter of the refrigerant compressor;
• Determining a value X _{t1 of} the monitoring _parameter after a first period of time after the determination of the maximum value X _max ;
• Detection of a blocked valve when X _{t1 is} less than X _max and (X _max - X _t1 ) / X _max ≥ Δ _X , where Δ _{X is} specified.

In particular, the blocked valve may be a blocked suction or pressure valve. In practice, the blockage condition can also be triggered by another defective element in the cooling circuit, such as a solenoid valve, which element does not necessarily have to be part of the refrigerant compressor. As already described above, this has in the blocking state in general but then a blocked valve of the refrigerant compressor, in particular a blocked pressure valve of Refrigerant compressor result, the blocked valve, the mass flow of the refrigerant largely, preferably completely blocked.

Continued running of the electric motor with maximum speed is caused in the application by an application device driving the coolant compressor, eg by a refrigerator, because the application device determines that the desired cooling does not occur and thus continues to demand maximum cooling capacity. A typical value for the maximum speed would be 3000 min ^-1 to 4000 min ^-1. It should be noted that it is clearly a refrigerant compressor with variable speed, otherwise only a single speed would be provided in the operation of the refrigerant compressor, which then also represented the maximum speed.

Certain minimal variations in speed are unavoidable in practice. Therefore, it makes sense to assume a certain tolerance range around the maximum speed value, typically a maximum of ± 2%. If the speed changes so that it deviates more strongly from the maximum speed value, in particular by more than 2% less than the maximum speed value, the process is interrupted. In the case of an increasing speed, the actual maximum speed value had not yet been reached, and the procedure is usually restarted when the actual maximum speed value is reached. In the case of a falling speed is typically assumed that the blocking situation or the blocked valve was no longer available, it could thus come to the desired cooling and the application device requested a lower cooling capacity. The process is thus interrupted and only restarted when the maximum speed is reached again.

As already noted, the extent to which the monitoring parameter decreases over time depends on the particular type of refrigerant compressor. It is provided in a preferred embodiment of the method according to the invention that Δ _X ≥ 0.2, preferably Δ _X ≥ 0.4, particularly preferably Δ _X ≥ 0.5 applies. This means that the percentage decrease in the value of the monitoring parameter must be at least 20%, preferably at least 40%, particularly preferably at least 50%.

As already stated, the monitoring parameter which has the described temporal behavior in the blockade state can be the current consumed by the electric motor. Similarly, a motor winding temperature and a temperature of a control electronics of the electric motor or the refrigerant compressor on the same temperature behavior, which is why these temperatures are ideal as monitoring parameters. In a preferred embodiment of the method according to the invention, it is therefore provided that the monitoring parameter is a current absorbed by the electric motor or a temperature of a control electronics of the refrigerant compressor, in particular of the electric motor, or of a motor winding of the electric motor. Clearly, these temperatures should always be given relative to the ambient temperature of the refrigerant compressor. If, for example, the ambient temperature is 20 ° C (room temperature) and the maximum value of the temperature is 90 ° C, 70 ° C must be used for X _max .

As determined in extensive experiments, it is advisable to carry out the determination of the maximum value X _max not immediately after the detection of the maximum speed of the electric motor, but hereby to wait a certain predetermined time. This allows a certain balance of pressure conditions to be established, for which the

Monitoring parameter can initially assume its maximum value X _max . Otherwise, there is a risk that the value of the monitoring parameter will increase even further until the equilibrium of the pressure conditions is reached. Therefore, it is provided in a preferred embodiment of the method according to the invention that the determination of the maximum value X _{max occurs} only after an initiation period after detection of the maximum speed of the electric motor. In other words, the detection of the maximum speed defines a start time or a start time for the method. In the mentioned preferred embodiment, immediately after the start time or after the start time, the initiation time interval is awaited before the determination of the maximum value X _{max of} the monitoring parameter is performed.

The optimum initiation time span can be determined in the trial for different refrigerant compressor types and then set accordingly, with the initiation period typically being a few minutes. It is therefore provided in a preferred embodiment of the method according to the invention that the initiation period is at least 5 minutes, preferably at least 10 minutes, more preferably at least 15 minutes.

In order to have the greatest possible certainty that the conditions for the blockage condition or for a blocked valve are actually met, a verification can take place in that the monitoring parameter is again determined shortly after its last determination and compared with the maximum value X _max . Even if this comparison indicates the blockage condition, it can be assumed with very high certainty that the blockage condition or a blocked valve is actually present. Therefore, it is provided in a preferred embodiment of the method according to the invention that after a verification period after the detection of the blocked valve, a value X _{t2 of} the

Monitoring parameter is determined and the detection of the blocked valve is verified when X _{t2 is} less than X _max and (X _max - X _t2 ) / X _max ≥ Δ _X applies. Waiting the verification period should thereby take into account any fluctuations in the monitoring parameter, ie if the value of the monitoring parameter is correspondingly low even after the verification period, it can be assumed with high probability that this reduction is not due to a random fluctuation.

Of course, particularly preferred embodiments are conceivable in which the condition (X _max - X _t2 ) / X _max ≥ Δ _X 'is checked for verification, where Δ _X ' ≠ Δ _X , preferably Δ _X '> Δ _X applies. This means that verification is carried out as to whether the monitoring parameter of the refrigerant compressor progresses in time as expected by model calculations and / or laboratory tests, with this development over time typically being a further decrease.

The optimal verification period may be determined in trial for different types of refrigerant compressor and then set accordingly, with the verification period typically being no more than a few minutes. Therefore, in a preferred embodiment of the method according to the invention, it is provided that the verification period is 15 s to 5 min, preferably 30 s to 3 min, particularly preferably 45 s to 1 min 30 s.

The first period of time may also depend on the type of refrigerant compressor and can be specified accordingly, in particular on the basis of experiments carried out. It is provided in a preferred embodiment of the method according to the invention that the first Time is at least 3 h, preferably at least 5 h, more preferably at least 6 h.

In a preferred embodiment of the method according to the invention, it is provided that after detection of the blocked valve, a corresponding error message is written in a readable memory provided therefor. Analogously, it is provided in a preferred embodiment of the method according to the invention that after verification of the detection of the blocked valve, a corresponding error message is written in a space provided, readable memory. The particular write to the read-only memory allows this information to be shared with different control systems - e.g. a control system of the application device - to provide for further processing. Furthermore, especially if it is a non-volatile memory such as e.g. a so-called FLASH, EPROM or NVRAM memory, the information is read out for diagnostic purposes even at a later date.

In practice, the detection or verification of the blockage or blocked valve can be used to shut off the compressor, since it is clear that in this state, the desired cooling can not be achieved. Continued running of the electric motor to maximum speed would therefore mean unnecessary loading of the compressor as well as unnecessary energy consumption. Accordingly, an operating method for operating a refrigerant compressor is provided according to the invention, the operating method comprising the inventive method, wherein after the detection of the blocked valve, the electric motor is stopped. Analogously, an operating method for operating a refrigerant compressor is provided according to the invention, the operating method comprising the method according to the invention, wherein after the verification of Detection of the blocked valve of the electric motor is stopped. Preferably, the electric motor in the stopped state does not absorb electricity, so that no unnecessary energy consumption takes place.

Experiments have shown that the cause of the blockage situation sometimes no longer exists after a restart of the refrigerant compressor. For example, it could be that a solenoid valve had triggered the blocking situation because it had not opened and thus blocked the cooling circuit, and that this solenoid valve now opens as planned when it is restarted. Therefore, it is provided in a preferred embodiment of the operating method according to the invention that the electric motor is restarted after a second period of time. Waiting for the second period of time can serve to bring about a certain relaxation of the pressure conditions, which can contribute to the release of a blocked valve. Furthermore, a temperature of the compressor may also relax during the second time period, which may also contribute to releasing a blocked valve.

In particular, if the blocking valve has an erratic behavior and blocked accordingly in some runs of the refrigerant compressor and not again in other runs, the second period of time can be kept relatively short, especially in the second range. It is therefore provided in a preferred embodiment of the operating method according to the invention that the second time period is at least 3 s, preferably at least 6 s, particularly preferably at least 15 s. In general, however, it should be noted that the values for the second period may vary widely depending on the application.

In practice, it makes sense not to let the second period of time be arbitrarily long, because of course Error conditions may occur in which a blocked valve no longer triggers. Therefore, it is provided in a particularly preferred embodiment of the operating method according to the invention that the second time period is a maximum of 60 minutes. That is, it is assumed that the blocking valve must solve within this maximum duration of the second period of time, otherwise it can be assumed that there is a fault condition in which the blocking valve no longer releases.

Analogous to the above, it is in a control system for a refrigerant compressor, the refrigerant compressor comprising a drive unit and a piston-cylinder unit for cyclically compressing a refrigerant, wherein the drive unit comprises an electric motor for driving the piston-cylinder unit and wherein the control system Control electronics, according to the invention provided that the control electronics for implementing a method according to the invention and / or for carrying out an operating method according to the invention is set up.

Finally, in order to be able to provide a refrigerant compressor which can reliably detect and respond to a stalled valve, it is in a refrigerant compressor having a drive unit and a piston-cylinder unit for cyclically compressing a refrigerant, the drive unit having a Electric motor for driving the piston-cylinder unit, according to the invention provided that the refrigerant compressor comprises a control system according to the invention.

It should be noted that in all of the above embodiments, the refrigerant compressor is, in particular, a refrigerant compressor having a hermetically sealed casing can act, wherein the drive unit and the piston-cylinder unit are arranged in the housing.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be explained in more detail with reference to an embodiment. The drawings are exemplary and are intended to illustrate the inventive idea, but in no way restrict it or even reproduce it.

Fig. 1

eine schematische axonometrische Ansicht eines erfindungsgemäßen Kältemittelkompressors mit abgenommener oberer Gehäusehälfte

Fig. 2

eine diagrammatische Veranschaulichung des erfindungsgemäßen Verfahrens

Showing:

Fig. 1

a schematic axonometric view of a refrigerant compressor according to the invention with removed upper housing half

Fig. 2

a diagrammatic illustration of the method according to the invention

WAYS FOR CARRYING OUT THE INVENTION

Fig. 1 shows a refrigerant compressor 1 according to the invention, wherein a hermetically sealed housing 2 of the refrigerant compressor 1 is only partially shown or an upper half of the housing 2 is removed to allow a view into the housing 2. Inside the housing 2, a cylinder housing 3 of a piston-cylinder unit can be seen. The cylinder housing 3 is mounted on a drive unit 4, which comprises an electric motor for driving the piston-cylinder unit. In this case, the electric motor via a crankshaft 10 and a connecting rod drives a piston of the piston-cylinder unit in a cylinder, which cylinder is arranged in the cylinder housing 3. As a result, a cyclical movement of the piston in the cylinder along a cylinder axis is realized in order to compress refrigerant.

The refrigerant is sucked via a suction muffler 9 and arranged in a valve plate 6 suction valve into the cylinder, compressed and passed through a arranged in the valve plate 6 pressure valve in an outwardly leading pressure tube 8. The refrigerant is subsequently conveyed in a refrigerant circuit of an application device, such as e.g. a refrigerator, in which refrigerant circuit of the refrigerant compressor 1 is incorporated, to a condenser (not shown) passed.

The valve plate 6 is mounted on the cylinder in the region of a cylinder head, wherein in Fig. 1 a cylinder cover 5 can be seen, which is screwed by means of screws 7 with the cylinder. The valve plate 6 is arranged between the cylinder cover 5 and the cylinder.

The refrigerant compressor 1 is operated at variable speed ω, that is, the rotational speed ω of the electric motor is dependent on the cooling capacity requested by the application device. With maximum cooling performance of the electric motor running at a maximum speed ω _max, which typically min ^-1 to 4000 min ^-1 3000.

In a blockage state, the mass flow of the refrigerant in the cooling circuit is greatly reduced or comes to a complete standstill. The blockage condition can be caused by a blocked valve of the refrigerant compressor 1 or leads to a blocked valve of the refrigerant compressor 1, since the valve, in particular the pressure valve, can no longer open properly due to the build-up pressure conditions. The latter means that the pressure built up by the piston-cylinder unit is not large enough to overcome the back pressure built up due to the blockage condition.

In order to reliably detect the blockage condition or a blocked valve, it is provided according to the invention that, in addition to the rotational speed ω, monitoring parameters of the refrigerant compressor 1 are continuously monitored in order to determine their time profile. In particular, a current I picked up by the electric motor and a temperature T of control electronics of the refrigerant compressor 1 or the electric motor or a motor winding of the electric motor are possible monitoring parameters. Clearly, these temperatures should always be given relative to the ambient temperature (typically room temperature or 20 ° C) of the refrigerant compressor.

• Bestimmung eines Maximalwerts X_max des Überwachungsparameters des Kältemittelkompressors 1;
• Bestimmung eines Werts X_t1 des Überwachungsparameters nach einer ersten Zeitspanne t1 nach der Bestimmung des Maximalwerts X_max;
• Detektion eines blockierten Ventils, wenn X_t1 kleiner als X_max ist und (X_max - X_t1)/ X_max ≥ Δ_X gilt, wobei Δ_X vorgegeben ist.

According to the following steps are performed after detection of the maximum speed ω _max , as long as the speed ω of the electric motor substantially corresponds to the maximum speed ω _max :

• Determining a maximum value X _{max of} the monitoring parameter of the refrigerant compressor 1;
• Determining a value X _{t1 of} the monitoring _parameter after a first period of time t1 after determining the maximum value X _max ;
• Detection of a blocked valve when X _{t1 is} less than X _max and (X _max - X _t1 ) / X _max ≥ Δ _X , where Δ _{X is} specified.

Fig. 2 illustrates these method steps based on the diagrammatic representation of the course of I and T as a function of time t. Directly below this diagram, the time profile of the rotational speed ω of the electric motor is shown. In this case, in the illustrated embodiment of the method according to the invention after the first detection of the maximum speed ω _max, first a predefinable initiation time period t0 is waited for, so that a certain equilibrium of the pressure ratios can be established before X _max is determined. Typically, t0 is at least 5 minutes, preferably at least 10 minutes, more preferably at least 15 minutes.

In a typical application analogous to Fig. 2 For example, the current I after the initiation period t0 has risen to a value of X _max = 0.85 A. Analogously, in such a typical application case, the temperature T after the initiation period t0 has risen to a value which, for example, gives X _max = 70 ° C. (corresponds to measured 90 ° C. at 20 ° C. ambient temperature).

The determination of X _t1 takes place after the first time period t1 has elapsed after the determination of X _max , t1 typically being at least 3 h, preferably at least 5 h, particularly preferably at least 6 h. That is, the time elapsed between the first detection of the maximum speed ω _max and the determination of X _t1 is t0 + t1. In a typical application analogous to Fig. 2 After the first period of time t1, the current I has fallen to a value of X _t1 = 0.425 A or, for example, to a value which corresponds to a relative reduction of 20% to 50%. Analogously, in such a typical application, the temperature T after the first time period t1 has dropped to a value which, for example, gives X _t1 = 50 ° C. (corresponds to measured 70 ° C. at 20 ° C. ambient temperature).

Depending on the type of the refrigerant compressor 1, a specific value for Δ _{X can be} specified, wherein typically Δ _X ≥ 0.2, preferably Δ _X ≥ 0.4, particularly preferably Δ _X ≥ 0.5 applies. The value suitable for the respective type can preferably be determined in a laboratory experiment. In the illustrated embodiment of the Fig. 2 is (X _max - X _t1 ) / X _max ≈ 0.56. When inputting of Δ _X = 0,5 so a blocked valve or the lock state is detected.

In the embodiment of Fig. 2 For safety, verification of the blocked valve is carried out by _{waiting for} a relatively short verification period t2 after the determination of X _t1 , in order then again to determine a current value X _{t2 of} the monitoring parameter and the condition (X _{max -X t2} ) / X _max ≥ Δ _X. Typically, the verification period t2 is 15 seconds to 5 minutes, preferably 30 seconds to 3 minutes, more preferably 45 seconds to 1 minute 30 seconds.

In a typical application analogous to Fig. 2 the current I has dropped to a value of eg X _t2 = 0.23 A after the verification period t2. Analogously, in such a typical application, the temperature T after the verification period t2 has dropped to a value which, for example, gives X _t2 = 18.9 ° C. (corresponds to measured 38.9 ° C. at 20 ° C. ambient temperature).

In the illustrated embodiment of the Fig. 2 is (X _max - X _t2 ) / X _max ≈ 0.73. That is, with setting of Δ _X = 0.5 that is, the detection of the blocked valve previously will be confirmed or verified.

To carry out the described method, the refrigerant compressor 1, a control system with a control electronics, which control electronics is set up to carry out said method. Preferably, this control electronics also forms the above-mentioned control electronics of the electric motor.

In the embodiment of Fig. 2 the control electronics is further adapted to carry out an operating method according to the invention, according to which the electric motor is stopped after the verification of the blocked valve or the blocking state. Accordingly falls in the lower diagram of the Fig. 2 the speed ω from the maximum speed ω _max to 0.

After stopping the electric motor no longer receives current I, the temperature T of the control electronics or the motor winding, however, continues slowly (to the ambient temperature) from, which is why in Fig. 2 the course of T in the region after t2 is indicated by a dashed line.

Since the cause of the blockage situation sometimes no longer exists after a restart of the refrigerant compressor 1, the control electronics may be configured to restart the electric motor after a relatively short second time period t3. Typically, the second time period t3 is only a few seconds, for example at least 3 s, preferably at least 6 s, particularly preferably at least 15 s. In practice, the second period t3 is typically limited to a maximum of up to 60 minutes.

In the lower diagram of the Fig. 2 are indicated by dotted lines different situations after switching on the electric motor. One of these situations would be that the electric motor again runs at the maximum speed ω _max , which will be the case in particular if the blockage situation still exists. In such a case, the inventive method described for detecting a blocked valve would be restarted immediately by the detection of the maximum speed ω _max .

In particular, if the blocking situation is no longer present, but can also occur situations in which the speed ω of the electric motor is below the maximum speed ω _max . In such a case, the described inventive method for the detection of a blocked valve would not but only again as soon as the maximum speed ω _max is subsequently detected.

It should be noted that the control system may have a memory in which after the detection or verification of the blockage condition, a corresponding error message is written, which error message can then be read out of the memory, in particular for diagnostic purposes. Furthermore, the memory on the deposit of retrieved during the inventive process or method of operation values can, in particular for the deposit of the values of Δ _X, t0, t1, t2 and t3 are used for the specific present refrigerant compressor. 1

LIST OF REFERENCE NUMBERS

1

Refrigerant compressor

2

Housing of the refrigerant compressor

3

cylinder housing

4

drive unit

5

cylinder cover

6

valve plate

7

screw

8th

Outward leading pressure pipe

9

suction silencer

10

crankshaft

I

Power absorbed by the electric motor

T

Temperature of a control electronics of the electric motor or a motor winding of the electric motor

t

Time

t0

Initiation period

t1

First time span

t2

Verification period

t3

second time span

ω

Speed of the electric motor

ω _max

Maximum speed of the electric motor

Claims (15)

1. Method for detection of a blocked valve of a coolant compressor (1) having a drive unit (4) and a piston/cylinder unit for cyclical compression of a coolant, wherein the drive unit (4) has an electric motor for drive of the piston/cylinder unit, wherein the speed of rotation (ω) of the electric motor is monitored, characterized in that first, a maximal speed of rotation (ω _max) of the electric motor is detected and that the following steps are carried out, as long as the speed of rotation (ω) of the electric motor essentially corresponds to the maximal speed of rotation (ω _max) :

   - determination of a maximal value X_max of a monitoring parameter (I, T) of the coolant compressor (1);

   - determination of a value X_t1 of the monitoring parameter (I, T) after a first time span (t1) after the determination of the maximal value X_max;

   - detection of a blocked valve, if X_t1 is less than X_max and (X_max - X_t1) / X_max ≥ Δ _X holds true, wherein Δ _X is predetermined.
2. Method according to claim 1, characterized in that Δ _X is ≥ 0.2, preferably Δ _X is ≥ 0.4, particularly preferably Δ _X is ≥ 0.5.
3. Method according to anyone of claims 1 to 2, characterized in that the monitoring parameter is a current (I) drawn by the electric motor or a temperature (T) of control electronics of the coolant compressor (1), particularly of the electric motor, or of a motor winding of the electric motor.
4. Method according to anyone of claims 1 to 3, characterized in that the determination of the maximal value X_max takes place only after an initiation time span (t0) after detection of the maximal speed of rotation (ω _max) of the electric motor.
5. Method according to claim 4, characterized in that the initiation time span (t0) amounts to at least 5 min, preferably at least 10 min, particularly preferably at least 15 min.
6. Method according to anyone of claims 1 to 5, characterized in that after a verification time span (t2) after detection of the blocked valve, a value X_t2 of the monitoring parameter (I, T) is determined, and detection of the blocked valve is verified if X_t2 is less than X_max and (X_max - X_t2) / X_max ≥ Δ _X holds true.
7. Method according to claim 6, characterized in that the verification time span (t2) amounts to 15 s to 5 min, preferably 30 s to 3 min, particularly preferably 45 s to 1 min 30 s.
8. Method according to anyone of claims 1 to 7, characterized in that the first time span (t1) amounts to at least 3 h, preferably at least 5 h, particularly preferably at least 6 h.
9. Method according to anyone of claims 1 to 8, characterized in that after detection of the blocked valve, a corresponding error message is written into a readable memory provided for this purpose.
10. Method according to anyone of claims 6 to 9, as long as they are dependent on claim 6, characterized in that after verification of the detection of the blocked valve, a corresponding error message is written into a readable memory provided for this purpose.
11. Operating method for operating a coolant compressor (1), the operating method comprising the method according to anyone of claims 1 to 10, wherein the electric motor is stopped after detection of the blocked valve.
12. Operating method for operating a coolant compressor (1), the operating method comprising the method according to anyone of claims 6 to 10, as long as they are dependent on claim 6, wherein the electric motor is stopped after verification of the detection of the blocked valve.
13. Operating method according to one of claims 11 to 12, characterized in that the electric motor is restarted after a second time span (t3), particularly wherein the second time span (t3) amounts to at least 3 s, preferably at least 6 s, particularly preferably at least 15 s, and/or maximally 60 min.
14. Control system for a coolant compressor (1), the coolant compressor (1) comprising a drive unit (4) and a piston/cylinder unit for cyclical compression of a coolant, wherein the drive unit (4) has an electric motor for drive of the piston/cylinder unit, and wherein the control system has control electronics, characterized in that the control electronics are set up for carrying out a method according to anyone of claims 1 to 10 and/or for carrying out an operating method according anyone of claims 11 to 13.
15. Coolant compressor (1) having a drive unit (4) and a piston/cylinder unit for cyclical compression of a coolant, wherein the drive unit (4) has an electric motor for drive of the piston/cylinder unit, characterized in that the coolant compressor (1) has a control system according to claim 14.

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