Method for determining health of oil circuit of oil-injected compressor

Abstract

According to an embodiment, there is disclosed a method for determining the health of an oil circuit (121) of an oil-injected compressor (102) for circulating oil as lubricant and coolant through compressor elements, the method comprising iteratively performing the following steps: measuring (200) ambient temperature, ambient pressure and / or ambient humidity levels; measuring (201) an injection temperature at a location (130) before the oil flows through the compressor element and an outlet temperature at a location (140) after the oil flows through the compressor element; estimating (213) an injection temperature and an exhaust temperature using a model describing the oil circuit (121) and based on values in the first set; calculating a deviation (214) between the measured (212) and the estimated (213) injection temperature, and a deviation (214) between the measured (212) and the estimated (213) discharge temperature; and wherein a health condition (216) is determined based on these deviations.

Description

Technical Field

[0001] The present invention relates to a method for determining the health of an oil circuit of an oil-injected compressor. Background Art

[0002] A compressor is a mechanical machine designed to provide gas (such as ambient air), compressed air under high pressure for use in industrial processes and / or medical applications. Depending on the required pressure, the desired application, the desired results and other prerequisites, one can choose from a variety of compressor technologies, such as axial compressors vs. centrifugal compressors, and oil-free compressors vs. oil-lubricated compressors.

[0003] Oil-lubricated screw compressors, also known as oil-injected screw compressors, are compressors that are lubricated with oil, which is used to lubricate the various mechanical parts of the compressor. In addition to the compressor elements, it can also lubricate bearings and gears.

[0004] The oil also has a cooling function. The compressed air is cooled with the help of a coolant (usually oil) in the compression space between the screws. The oil then circulates in a closed system (oil circuit), between the oil drum, the oil cooler and the compressor elements (in this case the screws), and mixes with the air before compression. This allows the operating temperature of the compressor to be controlled.

[0005] After compressing the air mixed with oil, the oil is separated from the compressed air in the oil separator. The compressed air then continues to flow through an aftercooler and then flows to the air tank to provide it to the user.

[0006] The separated oil is then pumped back into the oil circuit via the oil separator. This can be done with the aid of an oil pump, but can also be done by the compressor element itself through pressure-driven injection.

[0007] The closed oil circuit structure of the oil-injected compressor then comprises an oil cooler and, if necessary, an oil pump, a gearbox, compressor elements and an oil separator. In addition, there may be a bypass channel between the oil separator and the oil cooler, in which a portion is diverted to the oil cooler and a portion is directly returned to the oil circuit without flowing through the oil cooler. The diverted portion is then controlled by a thermostat. The thermostat then receives hot oil from the oil separator and then mixes the hot oil with the cooled oil from the oil cooler according to a certain mixing ratio to achieve the desired temperature. The cooled oil then contributes to improving the efficiency of the compressor, as well as lubricating the compressor elements and bearings, as mentioned above. The viscosity must be low enough so that sufficient flow of the oil can be guaranteed. The thermostat then also ensures that condensate is prevented from forming, which occurs when the temperature reaches the dew point of humid air. Condensate can lead to accelerated aging of the oil and the metal of the compressor.

[0008] It is noted that different configurations are possible. However, in order to guarantee the correct operation of the compressor, it must be understood that the correct operation of the oil circuit is essential in any configuration. However, as with any mechanical machine, over time, some form of degradation is inevitable due to, in particular, the presence of rotating parts, contamination in the ambient air surrounding the machine, exposure to large temperature differences, loss of oil and other internal or external influences that can prevent and / or impair the correct operation of the compressor.

[0009] Important components of the oil circuit are the oil cooler and the thermostat, since their degradation directly affects the temperature of the oil. A malfunctioning oil cooler and / or thermostat will lead to excessively high operating temperatures, which affects the aging of the oil and mechanical components. In addition, in the event that the operating temperature becomes too high, the machine will shut down to prevent spontaneous combustion of the oil. On the other hand, a malfunctioning thermostat can also lead to too low an operating temperature. This in turn can lead to the formation of condensate, which can lead to chemical degradation of the oil, as well as degradation of the material (e.g., metal) from which the oil cooler is made.

[0010] Traditionally, maintenance plans are drawn up based on a predefined number of permissible operating hours for the compressor. After the expiration of the permissible operating hours, the oil is preventively refilled and / or replaced. However, this does not take into account the actual condition of the compressor and the environment in which the compressor is installed. In addition, there is an increasing use of high-quality synthetic oils, which generally have a longer service life. Therefore, it is becoming increasingly important to be able to make a good estimate of the available oil volume in the oil circuit. This can potentially extend the intervals between changes and / or refills, which has the advantage of reducing maintenance costs. However, this requires proper monitoring of the compressor. It should also be understood that proper monitoring of the compressor may also include monitoring other aging processes, such as degradation of the oil quality or other components in the oil circuit.

[0011] Therefore, there is a need for a method for determining the technical condition or health of the oil circuit of an oil injected compressor.

[0012] It is therefore an object of the present invention to provide a method for monitoring a compressor and a support device for such a compressor. Summary of the invention

[0013] According to the present invention, the above object is achieved by providing, according to a first aspect of the present invention, a computer-implemented method according to the first claim, the method for determining the health of an oil circuit of an oil-injected compressor, the oil circuit comprising an oil cooler, an oil separator and a thermostat, the thermostat being configured to mix oil from the oil separator with oil from the oil cooler based on a predefined mixing ratio, the oil circuit being configured to circulate the oil as a lubricant and a coolant through compressor elements of the compressor, the method comprising iteratively performing the following steps:

[0014] - measuring the values ​​of quantities from a first group, the first group comprising the ambient temperature, the ambient pressure, the ambient humidity level, the rotational speed of a compressor element, the rotational speed of a fan of the oil circuit (if present) and / or the setting position of an active thermostat (if present);

[0015] -Measure the values ​​of quantities in the second group, including:

[0016] o a first temperature, the injection temperature at a location before the oil flows through the compressor element;

[0017] as well as

[0018] o a second temperature, the outlet temperature at a location after the oil has flowed through the compressor element;

[0019] - using a model describing the oil circuit and based on the values ​​in the first set, estimating the values ​​of the quantities in the second set;

[0020] - calculating a first deviation between the measured and estimated injection temperature, and a second deviation between the measured and estimated discharge temperature; and

[0021] The health status is determined based on the first deviation and the second deviation.

[0022] A measuring step is understood to mean the quantitative entry of the value of a quantity obtained from one or more observations, recordings or samplings at a specific measurement location with the aid of a suitable measuring instrument (such as a sensor) which serves to express the observed quantity as a number with relevant units that can be compared with other values ​​of the same quantity.

[0023] The estimation step is understood to mean determining the values ​​of quantities that are part of the second group based on the values ​​of quantities that are part of the first group using a scientific and / or mathematical model representing the technical process and / or the device, said model having as input the values ​​of the quantities that are part of the first group and having as output the values ​​of the quantities of the second group that have to be determined and therefore estimated based on one or more calculations.

[0024] The oil circuit is an oil circuit known in the prior art and is suitable for an oil-injected compressor, preferably a screw compressor. In a simple embodiment, it includes an oil cooler to cool the oil before it flows through the compressor element. "Flow" also includes "stream", "pass" or other terms that clearly indicate that the oil circulates in the circuit and then, for example, is sprayed into the compressor chamber in the form of a mist. Therefore, the term "flow" includes atomizing the oil for further circulation. The oil circuit also includes an oil separator after the compressor element, that is, at a position in the circuit after the oil flows through the compressor element. The oil separator is configured to extract oil from the compressed air, as known in the prior art. In addition, the oil circuit may also optionally include an oil pump to circulate the oil in the circuit. Alternatively, in the absence of an oil pump, the oil circulates in the circuit based on pressure-driven injection by the compressor element itself.

[0025] The oil circuit also includes a thermostat. The thermostat is configured to mix the hot oil from the oil separator with the cooled oil from the oil cooling system based on a certain mixing ratio to obtain a desired temperature of the oil injected into the compressor element. The thermostat can be active or passive.

[0026] Active thermostats have an actively controlled valve which is controlled so that at a certain mixing ratio the oil from the oil separator is mixed with the oil from the oil circuit so that the injection temperature reaches a predefined temperature. For passively controlled valves, the valve is mechanically controlled using a bimetallic strip and the injection temperature is generated based on the set mixing temperature as long as the temperature of the cooled oil is below the desired mixing temperature.

[0027] When the oil circuit includes an active thermostat and an oil separator, according to an embodiment, the thermostat is configured to mix oil from the oil separator with oil from the oil cooler based on a mixing ratio. Here, the method further includes the step of measuring a setting position of the active thermostat, and wherein the health condition is further determined based on the setting position.

[0028] When the oil circuit includes a passive thermostat and an oil separator, the method according to an embodiment further includes the step of measuring a third temperature (cooling temperature) at a position after the oil flows through the oil cooler, and the health condition is further determined based on the cooling temperature. It should be noted that the embodiment can also be applied to an active thermostat when the effective setting position cannot be measured.

[0029] An unexpectedly high injection temperature can therefore be directly related to a malfunctioning thermostat. In other words, a thermostat problem can be distinguished in this way from an oil cooler problem and / or a problem of too low a flow rate, quality or volume in the oil circuit. For an active thermostat, it is necessary to know the actual position of the thermostat valve, or, as mentioned above, if it is not possible to know the actual position of the thermostat valve by measuring the temperature of the cooled oil. Since this is not possible with a passive thermostat, the cooled oil temperature is measured here.

[0030] The basic concept is that the oil flows from the oil separator to the oil circuit, through the compressor elements, and then flows to the oil separator again, so that the oil acts as a lubricant and coolant for the oil-injected compressors known in the prior art. It should also be understood that there are other components along the oil circuit, such as the gearbox explained above, the thermostat, and the oil also flows through one or more bearings of the engine.

[0031] According to the method, the temperature of the oil is measured at various locations along the oil circuit to infer or determine the health of the oil circuit.

[0032] The first location to measure the temperature is before the oil flows through one or more compressor elements. The temperature measured here is also referred to as the injection temperature. It should also be understood that, for practical reasons, the location may also be as close as possible to the point where the oil is introduced into one or more compressor elements.

[0033] The second location where the temperature is measured is after the oil has flowed through one or more compressor elements. The temperature is also referred to as the discharge temperature. Again, for practical reasons, the location may be a location close to the point where the oil leaves one or more compressor elements.

[0034] Due to the thermodynamic process of the compressor element compressing air or other gas into compressed air or compressed gas, the air or gas will heat up. By allowing the oil to flow through the compressor element during the compression, the generated heat can be absorbed by the oil. Therefore, it should be understood that the temperature of the oil before flowing through the compressor element determines the heat that can be absorbed.

[0035] Furthermore, the expected values ​​of the second set of variables, such as the injection temperature and the discharge temperature, are estimated based on a static model, respectively. The model is a scientific and / or mathematical model and represents the combination of the compressor and the oil circuit. The model is, for example, a set of equations and / or empirical relationships that describe the different physical components of the compressor and the oil cooler and relate to each other by means of one or more common quantities.

[0036] Since the model represents the compressor, or more specifically the oil circuit, the expected injection temperature and outlet temperature can be estimated based on the model in combination with the ambient temperature. This can also be explained as follows. The model includes the value of the nominal power of the compressor, thereby allowing the heat generated due to compression in the nominal state to be inferred. In addition, the model will also include the cooling capacity of the oil circuit, which corresponds to the heat that can be removed in the nominal state. If the temperature of the environment in which the compressor is installed is also considered, the expected injection temperature and outlet temperature can be inferred. In other words, according to the embodiment, these temperatures can be determined if it is assumed that the compressor is running in the nominal state. In order to improve the accuracy of the estimate, they are then further determined based on other quantities in the first group that indicate operating conditions and / or environmental conditions. These variables are ambient temperature, ambient pressure, ambient humidity level, rotation speed of compressor elements, rotation speed of cooling circuit fan (if present) and / or setting position of active thermostat (if present).

[0037] By means of these disclosed steps of the method according to the invention, it will be understood that in this way, the increase in temperature of the oil as it passes through the compressor elements and therefore the amount of heat absorbed during compression is indirectly determined.

[0038] However, the inventors have discovered that in addition to simply analyzing the temperature increase of the oil as it passes through the compressor elements, these measurements can also be used to infer the health of the oil circuit, and more specifically, the oil flow rate, oil quality and oil volume in the oil circuit, as well as the degree of blockage of the oil cooler and whether the thermostat is working correctly.

[0039] The oil cooling system is connected to the oil circuit via a primary circuit so that oil flows through the primary circuit. Thus, when the oil cooling system is connected to the oil circuit, the primary circuit forms an integral part of the oil circuit. Furthermore, the oil cooling system has a secondary circuit through which a coolant flows in order to extract heat from the oil flowing in the primary circuit and transfer the heat to the environment. Since the oil cannot mix with the coolant, the primary circuit and the secondary circuit are separated from one another, whereby the combination of the two forms a heat exchanger. Furthermore, for the secondary circuit, a variety of cooling media can be used. According to an embodiment, the coolant is ambient air around the compressor, whereby the coolant then flows through the secondary circuit via a forced flow by means of a fan. The oil cooling system also has an air side along which the ambient air flows.

[0040] However, the air side of the oil cooling system can become clogged due to dust particles and other air pollutants. This phenomenon is also called clogging, and the level at which it occurs is also called the degree of clogging.

[0041] Furthermore, a predefined mass or volume of oil should be present in the oil circuit to ensure that it functions as a lubricant and coolant under optimal conditions. The mass or volume then corresponds to a certain flow through the oil circuit. If the flow is below a predefined value, which in turn corresponds to a mass or volume that is too low, the functioning of the oil circuit is no longer guaranteed. As described above, based on the disclosed steps, it is also possible to subsequently determine the oil flow, the oil mass and / or the oil volume and thus the health of the oil cooling system.

[0042] As will be further explained, the inventors have found that based on the above steps, it is also possible to distinguish between three aspects of health, namely, too low oil flow, oil quality and / or oil volume, blockage on the air side of the oil cooler, and a malfunctioning thermostat.

[0043] The advantage of this is that the cause of a malfunction in the oil circuit can be reported before intervention. Low oil flow, oil quality or oil volume requires different forms of intervention than a highly clogged cooling system or a malfunctioning thermostat, so that intervention can be optimized through such reporting.

[0044] According to an embodiment of the invention, the estimation further comprises estimating one or more time-dependent quantities in a third group indicating the thermal inertia of the oil circuit and / or the transit time of the oil through the oil circuit, wherein the model further comprises differential equations and / or convolutions comprising time-dependent status variables comprising one or more quantities in the third group, and wherein the values ​​of the quantities in the second group are further estimated based on the estimated values ​​in the third group. The variables in the third group are the oil temperature at the outlet of the oil separator, the mass flow rate of the oil, the inlet pressure of the oil at the inlet of the oil cooler and / or the inlet temperature of the oil cooler.

[0045] By supplementing the static model with one or more time-dependent quantities from this third group, the thermal inertia of the oil circuit and / or the transport time of the oil through the oil circuit and the various components is taken into account. The quantities of the second and third groups will then be estimated at successive points in time using the update equations. The frequency or time step at which the estimation and updating take place in turn depends on the expected change of the corresponding quantity or quantities over time. This allows the number of calculations to be adjusted according to physical aspects. For the quantities in the second group, the results of these estimates are then compared with the measured values ​​of the quantities in the second group.

[0046] According to an embodiment, measuring the values ​​of the quantities in the second group also includes measuring a third temperature (the outlet temperature of the oil cooler), and the estimating also includes estimating the third temperature, and the calculating also includes calculating a third deviation between the measured third temperature and the estimated third temperature, and wherein the health status is further determined based on the third deviation.

[0047] Thus, the determination of the health condition may be further refined by estimating the exhaust temperature on the one hand and estimating the temperature on the other hand, and wherein the difference between the measurement and the estimation is then taken into account to determine the health condition.

[0048] According to an embodiment, the thermostat is an active thermostat and the method further comprises the step of measuring a setting position of the active thermostat and measuring a third temperature, an outlet temperature of the oil cooler, based on the measured setting position.

[0049] In other words, because there is a relationship between the setting position of the active thermostat and the outlet temperature of the oil cooler, this temperature can be measured indirectly. The setting value is then converted into said temperature and further used as a measurement.

[0050] According to a second aspect of the present invention, a data processing system is disclosed, the system comprising a processing unit configured to perform the method of the first aspect of the present invention.

[0051] According to a third aspect of the present invention, a computer program product comprising computer executable instructions is disclosed. When the program is run on a computer, the computer executable instructions are used to perform the method of the first aspect.

[0052] According to a fourth aspect of the present invention, a computer readable storage medium comprising the computer program product of the third aspect is disclosed.

[0053] According to a fifth aspect of the present invention, a compressor comprising the data processing system of the second aspect of the present invention is disclosed.

[0054] According to a sixth aspect of the present invention, a method for determining a health status of an oil circuit of an oil-injected compressor is disclosed, the oil circuit comprising an oil cooler, an oil separator, and a thermostat, the thermostat being configured to mix oil from the oil separator with oil from the oil cooler based on a predefined mixing ratio, the oil circuit being configured to circulate the oil as a lubricant and a coolant through compressor elements of the compressor, the method comprising iteratively performing the following steps:

[0055] - measuring the values ​​of quantities from a first group, the first group comprising the ambient temperature, the ambient pressure, the ambient humidity level, the rotational speed of a compressor element, the rotational speed of a fan of the oil circuit (if present) and / or the setting position of an active thermostat;

[0056] - measuring the values ​​of quantities in a second group, the second group comprising:

[0057] o a first temperature, the injection temperature at a location before the oil flows through the compressor element;

[0058] as well as

[0059] o a second temperature, the outlet temperature at a location after the oil has flowed through the compressor element;

[0060] - using a model describing the oil circuit and based on the values ​​in the first set, estimating the values ​​of the quantities in the second set;

[0061] - calculating a first deviation between the measured and estimated injection temperature, and a second deviation between the measured and estimated discharge temperature; and

[0062] The health status is determined based on the first deviation and the second deviation.

[0063] According to an embodiment, the estimation further comprises estimating one or more quantities in a third group indicating the thermal inertia of the oil circuit and / or the transit time of the oil through the oil circuit, wherein the model further comprises differential equations and / or convolutions comprising time-dependent state variables comprising one or more quantities in the third group, and wherein the values ​​of the quantities in the second group are further estimated based on the estimated values ​​in the third group.

[0064] The quantities in the third group include one of the group consisting of: oil temperature at the outlet of the oil separator, mass flow rate of the oil, inlet pressure of the oil at the inlet of the oil cooler, inlet temperature of the oil cooler.

[0065] According to an embodiment, the health condition is further determined using regression analysis, wherein the first and second deviations are explanatory variables and the health condition is a dependent variable.

[0066] According to an embodiment, the regression analysis model comprises one of the group consisting of: a support vector machine, a neural network, a non-linear regression including an analytical equation, a decision tree, a random forest, and / or a gradient boosting method.

[0067] According to an embodiment, the health condition comprises a blockage degree of the oil cooler and / or an oil flow rate below a predefined value and / or comprises a malfunctioning thermostat.

[0068] According to an embodiment, the estimation is also performed based on one or more setting parameters of the compressor.

[0069] According to an embodiment, the setting parameters comprise one or more of the group consisting of: pressure, flow rate, humidity level, power, rotation speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The present invention will be further described with reference to the accompanying drawings, in which

[0071] Figure 1 schematically illustrates an air-cooled, oil-injected screw compressor and associated peripheral equipment; and

[0072] Figure 2Schematically illustrating steps for determining the health of an air-cooled, oil-injected screw compressor according to an embodiment of the disclosed invention;

[0073] Figure 3 schematically illustrates a method for estimating a time-dependent quantity; and

[0074] Figure 4 The difference between the measured data and the estimated values ​​for the injection temperature and the discharge temperature respectively is shown;

[0075] Figure 5 Schematically illustrates the steps for determining the health of the oil circuit of an oil injected compressor; and

[0076] Figure 6 An overview of the different quantities for each group is provided. DETAILED DESCRIPTION

[0077] The present invention will be described with respect to certain embodiments and with reference to certain drawings, but the invention is not limited thereto and is determined solely by the claims. The drawings described are merely schematic and non-limiting. In the drawings, for illustrative purposes, the dimensions of certain elements may be exaggerated and not drawn to scale. Dimensions and relative dimensions do not necessarily correspond to actual practical embodiments of the present invention.

[0078] In addition, the terms "first", "second", "third", etc. are used in the description and claims to distinguish similar elements, and not necessarily to describe a sequential or chronological order. These terms are interchangeable under appropriate circumstances, and the embodiments of the invention may be practiced in sequences other than those described or illustrated herein.

[0079] Furthermore, the terms "above", "below", "over", "below", etc., used in the description and claims are for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances, and the embodiments of the invention described herein may be employed in orientations other than those described or illustrated herein.

[0080] Additionally, while various embodiments are referred to as "preferred embodiments," they are to be understood as exemplary means of carrying out the invention, and not as limitations on the scope of the invention.

[0081] The term "comprising" used in the claims should not be understood as being limited to the components or steps set forth below; the term does not exclude other elements or steps. The term should be interpreted as specifying the presence of the mentioned features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components or groups thereof. Therefore, the scope of the expression "a device comprising components A and B" should not be limited to devices consisting only of components A and B. The meaning is that, for the purposes of the present invention, only components A and B of the device are listed, and the claims are further understood to also include equivalents of these components.

[0082] Figure 1 An air-cooled, oil-injected screw compressor is schematically shown. In the schematic, four circuits are distinguished, namely an air circuit 120, an oil circuit 121, a water circuit 123 and a circuit 122 through which a mixture of air and oil flows. However, it should be understood that this represents an ideal situation, since in a practical embodiment, for example, the circuit 120 may still contain residual oil particles after compression, as will be explained later.

[0083] Operation can be described as follows. At the inlet 101, ambient air is sucked into the compressor 102 to be compressed. As will be further explained, the ambient air is mixed with oil before being compressed by the compressor 102. After the compressor 102, there is an oil separation container 104, from which the oil is pumped into the oil circuit 121 through the compressor element of the compressor 102. This is called pressure-driven injection. Thermostat 112 determines the temperature of the oil that is injected into the engine 113 and the associated gearbox and then injected into the compressor element of the compressor 102. Thermostat 112 receives hot oil directly from the oil separation container 104 and oil cooled by the oil cooler 110. Thermostat 112 further determines the mixing ratio between hot oil and cold oil to obtain the desired temperature of the oil injected into the compressor 102. The cooled oil from the oil cooler 110 is used to improve the efficiency of the compressor element, as well as to lubricate the compressor element and bearings. The viscosity must be kept high enough to ensure sufficient flow of the oil. Thermostat 112 must also prevent the formation of condensate by maintaining the temperature above the dew point of water. The presence of condensate can cause accelerated aging of the oil and metal of the compressor due to chemical reactions.

[0084] There are three main degradation mechanisms that often occur and should be monitored. The first degradation mechanism is a malfunction of the cooler pack (i.e., the air cooler 107 and the oil cooler 110). The second degradation mechanism is a drop in the oil level. The third degradation mechanism is a malfunction or failure of the thermostat. The latter means that the desired or set mixture ratio does not correspond to the actual mixture ratio.

[0085] Faulty cooler packs 107, 110 can be associated with increased clogging or a failed fan 111. Clogging of cooler packs 107, 110 is primarily related to the accumulation of dirt or dust on the air side of the coolers 107, 110. The oil level is reduced because a small portion of the oil is allowed to pass through the oil separation element 105. When the oil separation element 105 becomes clogged and / or contaminated, the oil entrainment also increases. In addition, leaks can occur in the system, which can cause additional oil losses. The maintenance plan for oil-injected compressors is based on the service life and availability of the oil in the machine. According to the prior art, the oil is replenished and / or replaced based on the number of operating hours, so the actual oil loss from the particulate machine is not taken into account. Due to the increasing use of high-quality synthetic oils, which remain suitable for use as coolants for a longer period of time than conventional oils, it is very important to have a good estimate of the amount of oil remaining available in the oil circuit 121 in a timely manner. Extending the intervals between changing and / or refilling the oil has the advantage of reducing maintenance costs. Therefore, this requires good monitoring.

[0086] A poorly functioning thermostat means that the mixing ratio for mixing the portion of hot oil diverted from the bypass channel to the oil cooler with the cooled oil from said oil cooler will be incorrectly set relative to the desired temperature. In other words, the oil temperature is either too high or too low compared to the desired temperature.

[0087] The oil circuit 121 is used to provide coolant and lubricant to the compressor elements of the compressor 102. Therefore, if the air sucked in at the inlet 101 is measured at the measuring point 130 to be within the prescribed specifications of the compressor 102, then an increase in the discharge temperature measured at the measuring point 140 can be considered as a major sign indicating a problem with the oil circuit 121. There are three main forms of degradation, as a result of which the outlet temperature measured at the measuring point 140 deviates from the value expected during normal operation of the compressor 102.

[0088] On the one hand, the temperature of the injected oil can be too high or too low, on the other hand, the flow rate of the injected oil can be too low. An injection temperature that is too high or too low can be measured directly, but in relation to a standard value under the same operating conditions. In other words, a model must be used to determine the deviation.

[0089] An oil flow that is too low cannot be measured directly but can be inferred based on the temperature measurements at the measuring points 130 and 140 .

[0090] refer to Figure 2 , which schematically illustrates the steps for determining the health of the air-cooled oil-injected screw compressor 102, will further explain how the above-mentioned degradation can be derived.

[0091] In a first step 200, the ambient temperature, ambient pressure and ambient humidity are measured and stored in module 210 for further processing. In a second step 201, which may occur simultaneously with step 200, the temperature at location 130 and the temperature at location 140 are measured. The first temperature is the injection temperature and the second temperature is the outlet temperature. These values ​​are then stored in module 211 for further processing. The injection temperature and the outlet temperature are then estimated in module 213 based on the values ​​measured in step 200.

[0092] For example, the injection temperature can be estimated from the temperature at the separator, the cooling air temperature, the oil flow rate and the fan speed, and then the outlet temperature can be estimated from the injection temperature, the inlet temperature, the oil flow rate and the speed of the compressor element.

[0093] Between blocks 212 and 213, the measured values ​​and the estimated values ​​can be compared to each other to determine a first deviation 214 between the measured and estimated injection temperature 130 and a second deviation 215 between the measured and estimated discharge temperature 140. A health condition can then be determined based on the two deviations 214 and 215, for example expressed as a value in block 216.

[0094] The values ​​of the injection temperature and the discharge temperature can be estimated by explicitly taking into account the time dependence of one or more quantities (for example, using differential equations). The first time derivative of the temperature at the outlet of the oil separator depends, for example, on the rotational speed of the compressor element, the pressure at the outlet and the difference between the outlet temperature and the temperature at the outlet of the oil separator.

[0095] Figure 3 A method for estimating such quantities, which may be the temperature at the outlet of the oil separator and / or the temperature at a location in the oil circuit that is difficult to measure, is schematically shown. These values ​​may be processed in module 310 as values ​​220 and then as input to module 213.

[0096] In the absence of an unexpected blockage in the oil circuit 121, an increased injection temperature may be associated with a malfunctioning thermostat 112 or cooler package 107, 110. A low oil flow may be associated with a low oil level in the oil separation container 104.

[0097] In order to differentiate a problem with the thermostat 112 from a problem with the cooler pack 107 , 110 , the actual position of the thermostat valve 112 may be measured, as well as the temperature of the cooled oil, ie, the temperature at position 150 .

[0098] refer to Figure 4 , we can infer where the problem lies. Figure 4The difference between the measured data and the estimated amount is shown, wherein the difference between the measured and estimated injection temperature 130 is shown on the horizontal axis and the difference between the measured and estimated discharge temperature 140 is shown on the vertical axis. This is related to the problem of too little oil in the oil circuit 121 in the zone 401 and the blockage of the cooler package 107, 110 in the zone 402.

[0099] refer to Figure 2 , which shows the Figure 4 The two deviations 214 and 215 also shown in FIG. 2 are used to determine the health condition, for example represented by the value in module 216 .

[0100] Figure 5 A scheme for assessing the health of the oil circuit 121 is shown. After measuring and estimating 500 the temperature, the condition can be determined. When the difference 501 between the estimation and the measurement of the discharge temperature 130 is less than a predefined value, it is inferred that the oil circuit 121 does not show deviations and therefore works optimally 502. If the difference 501 is larger, then in step 503 the difference between the measurement and the estimation of the injection temperature 140 is checked. If the difference 503 is less than a predefined value, then it means that the oil level is too low 504 and an instruction to refill the oil level 505 can be given. If the difference 503 is greater than a predefined value, then the difference 506 between the measurement and the estimation of the oil temperature at the outlet 150 of the oil separator is considered. When the difference 506 is less than a predefined value, it means that the thermostat is faulty 507. Otherwise, it means that the cooler pack is faulty due to increased clogging 508.

[0101] at last, Figure 6 It is an overview of the different quantities of each group. The first group 600 includes the measured quantity, but does not include the estimated quantity. These quantities include compressor element speed, oil circuit fan speed (if present), ambient temperature, ambient pressure, ambient humidity level and compressor outlet pressure. The second group 601 includes measured and estimated quantities. The quantity of the group includes the outlet temperature of the oil after the element, the injection temperature of the oil before the element and the outlet temperature of the oil at the oil cooler. Group 602 only includes the estimated quantity, so it does not include the measured quantity. These quantities include the oil temperature at the outlet of the oil separator, the mass flow of the oil, the inlet pressure of the oil at the inlet of the oil cooler and the inlet temperature of the oil cooler. In addition, the outlet temperature of the oil after the element (shown in reference numeral 604) and the inlet temperature of the oil cooler (shown in reference numeral 605) can be time-dependent. Therefore, reference numeral 603 indicates the time-dependent quantity. Therefore, reference numeral 603 points out the time-dependent quantity, and forms the third group of quantities as a collection of reference numerals 604 and 605.

Claims

1. A computer-implemented method for determining a health of an oil circuit (121) of an oil-injected compressor (102), the oil circuit (121) comprising an oil cooler (110), an oil separator (104), and a thermostat (112), the thermostat (112) being configured to mix oil from the oil separator (104) with oil from the oil cooler (110) based on a predefined mixing ratio, the oil circuit (121) being configured to circulate oil as a lubricant and a coolant through compressor elements of the compressor (102), the method comprising iteratively performing the following steps: - measuring (200) the values ​​of quantities in a first group, said first group comprising ambient temperature, ambient ambient pressure, ambient humidity level, speed of the compressor element, speed of the fan of the oil circuit (if present) and / or the setting position of the thermostat; - measuring (201) the value of a quantity in a second group, said second group comprising: o A first temperature, at the injection nozzle at a location (130) before the oil flows through the compressor element. Inlet temperature; as well as o A second temperature, at a location (140) after the oil has flowed through the compressor element Mouth temperature; - using a model describing the oil circuit (121) and based on the values ​​in the first set, estimating (213) the values ​​of the quantities in the second set; - Calculation of a first deviation between the measured (212) and estimated (213) injection temperature (214), and the measured (212) and estimated (213) discharge temperatures a second deviation (215); and The health status (216) is determined based on the first deviation (214) and the second deviation (215).

2. A computer-implemented method according to claim 1, wherein the estimating (213) further comprises estimating one or more quantities in a third group (220) indicative of the thermal inertia of the oil circuit and / or the transit time of the oil through the oil circuit, wherein the model further comprises differential equations and / or convolutions comprising time-dependent condition variables comprising one or more quantities in the third group, and wherein the values ​​of the quantities in the second group are further estimated based on the estimated values ​​in the third group.

3. The computer-implemented method of claim 2, wherein the amounts in the third group include one of the group consisting of: - oil temperature at the outlet of the oil separator (104); - oil mass flow rate; - the inlet pressure of the oil at the inlet of the oil cooler; - Oil cooler inlet temperature.

4. A computer-implemented method according to any of the preceding claims, wherein the health condition (216) is further determined using a regression analysis, wherein the first deviation (214) and the second deviation (215) are explanatory variables and the health condition (216) is the dependent variable.

5. The computer-implemented method of claim 4, wherein the regression analysis model comprises one of the group consisting of: a support vector machine, a neural network, a nonlinear regression including an analytical equation, a decision tree, a random forest, and / or a gradient boosting method.

6. The computer-implemented method of any of the preceding claims, measuring (201) values ​​of quantities in a second set, the second set further comprising: - The third temperature, oil cooler outlet temperature (150), And wherein the estimating further comprises estimating a third temperature, and the calculating further comprises calculating a third deviation between the measured and estimated third temperatures, and wherein the health condition is further determined based on the third deviation.

7. The computer-implemented method of claim 6, wherein the thermostat is an active thermostat (112), the method further comprising the steps of: - measuring the setting position (305) of the active thermostat (112); And wherein measuring the third temperature is performed based on the measurement setting position (305).

8. The computer-implemented method of any one of the preceding claims, wherein the health status (216) comprises: The degree of clogging of the oil cooler (110), and / or an oil flow rate below a predefined value, and / or a malfunctioning thermostat.

9. The computer-implemented method of any of the preceding claims, wherein the estimating is further performed based on one or more setting parameters of the compressor (102).

10. The computer-implemented method of claim 9, the adjusting parameters comprising one or more of the group consisting of: pressure, flow rate, humidity level, power, rotation speed.

11. A data processing system comprising a processing unit configured to perform the method according to any of the preceding claims.

12. A computer program product comprising computer executable instructions for executing the method according to any one of claims 1 to 10 when the program is run on a computer.

13. A computer-readable storage medium comprising the computer program product according to claim 12.

14. A compressor (102) comprising the data processing system according to claim 11.

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