EP3483529B1

EP3483529B1 - Lubricant monitoring system for a circuit compressor

Info

Publication number: EP3483529B1
Application number: EP18205135.9A
Authority: EP
Inventors: Giuseppe Vitri; Giampietro SCAVOLINI
Original assignee: Rivacold Srl
Current assignee: Rivacold Srl
Priority date: 2017-11-09
Filing date: 2018-11-08
Publication date: 2020-09-30
Anticipated expiration: 2038-11-08
Also published as: SI3483529T1; EP3483529A1; PL3483529T3; HRP20201925T1; DK3483529T3; ES2834887T3; PT3483529T

Description

The present invention relates to lubricant monitoring system of a compressor of a refrigerating circuit particularly but not exclusively suitable for hermetic compressors and not of a refrigerating circuit.
There are known refrigerant circuits provided with hermetic rotary compressors such as the rotary vane compressor where the cylindrical piston rotating about its own geometric axis is provided with at least one radially movable vane and rotates inside a cylindrical seat offset with respect to the rotation and geometric axis of the piston and where the chambers delimited by one or two adjacent vanes and by the facing cylindrical surfaces of the chamber and of the piston have a volume which cyclically passes from a maximum value to a minimum value; said chamber is provided with an inlet, or a suction or intake port, and of an exit, or a delivery port, positioned so as to take advantage of room volume changes to compress incoming gas.
There are also known refrigerant circuits with rolling piston hermetic compressor; this type of compressor has a cylindrical piston rotating around a rotation axis parallel and spaced from the geometric axis of the piston itself which rotates while remaining tangent to the surface to its cylindrical seat provided with intake or suction and output or delivery ports where the latter is equipped with a non-return valve, between these ports a sliding housing is obtained for a movable vane which slides with the cylindrical surface of the piston.
This type of hermetic compressors and other types of hermetic and non-hermetic compressors are often without any checking means of lubricating oil level, for example of a transparent window type, a rod, a level sensor or oil pressure lubricant, etc.
Other types of compressors for refrigeration systems may be equipped with means for checking the oil level, but these means may be placed in positions that are inaccessible or the plant may not be guarded by personnel assigned to check the oil level.
A disadvantage of such known systems and compressors consists in that the lack of oil verification means or of direct control of said means can lead to their operation with an insufficient oil (or lubricant in general) level or quantity so causing a very rapid deterioration and seizure of compressor with consequent plant shutdown, so that, in addition to requiring the replacement or repair of compressor, may cause deterioration of goods or materials whose conservation or proper functioning was entrusted to the plant itself.
An object of the present invention is to propose a lubricant monitoring system of a compressor of a refrigerating circuit applied to lubricated compressors of hermetic and non-hermetic type, of eccentric piston type, of rotary piston, of reciprocating piston, and similar compressors or of any other type, without needing the internal access to compressor for checking the lubricant state or presence and without physical intervention on the compressor itself.
Another object is to propose a system fit for emitting alarm signals of any kind, even digital and remotely, in case of insufficient lubricant quantity.
A further object is to propose a system capable of deactivating and/or switching off the compressor whose lubricant level is insufficient.
Another object is to propose a system that can be implemented both in new plants and on already installed systems.
A further object is to propose a system that is also suitable for compressors in systems equipped with several compressors, with sections at low, medium and high temperatures and in heat pump systems.
Prior art document N. US 5 209 076 A refers to a system for monitoring a compressor.
Said compressor 10 has a sensor detecting the lubricant oil pressure (element 44 of figure 1 of document N. US 5 209 076 A ) for providing the system with oil pressure data used by the system to detect abnormal conditions of the lubricant oil or troubles and to generate an alarm when said abnormal conditions occur. Moreover, US 5 209 076 A discloses a monitoring system according to the preamble of claim 1.
The oil check, (option 132, conditional step 134 of figure 3 and diagram of figure 6 of document N. US 5 209 076 A ) provides, as at lines 56-60 of column 3 of document N. US 5 209 076 A , the use of a pressure transducer 44 sensing the pressure of the lubricating oil that is used for lubrication of the compressor 10 and provides oil pressure information to the device 38. Said system generates an alarm if the oil pressure doesn't reach or overpass a preset threshold within a predetermined time span, as in manostat, but without providing any indications related to lubricant oil if the compressor is not provided from the beginning or has an internal sensor of the lubricant pressure.
The possible outlet compressed gas pressure sensor of document N. US 5 209 076 A is provided for stopping the compressor in case of high pressure (fig. 7 of document N. US 5 209 076 A ) and it doesn't cooperate to oil checking.
Prior art document N. WO 96/39601 A1 refers to an apparatus and method to determine and to control the oil level in one or more refrigeration system compressors (14, 18). The invention of document WO 96/39601 A1 returns lubricating oil to compressors to maintain oil levels sufficient for proper lubrication of each compressor, and also monitors the flow rate of oil returned to each individual compressor. A level sensor (93, 94) and a flow control device (88) are connected to a control circuit (56) to control the flow of lubricating oil returning to the compressors.
Prior art document EP 2 690 379 A1 refers to a heat pump circuit whose output gas pressure is continuously (during the compressor operative condition) monitored to detect possible instability thereof and to provide information on possible oil trapping into the circuit, but without detecting a possible lack of oil quantity
According to the invention a monitoring system according to claim 1 is provided. Further embodiments are defined in the dependent claims. The characteristics of the invention are shown below with particular reference to the attached drawings in which:

Figure 1 shows a schematic view of the lubricant monitoring system of a compressor of a refrigerating circuit object of the present invention;
Figure 2 shows on a Cartesian plane, where the abscissa axis is time and the ordinates axis is the pressure at delivery of a compressor of a refrigeration circuit of Figure 1 starting just before the compressor stop and in a condition of maximum level of the compressor lubricant;
Figure 3 shows on the Cartesian plane similar to that of Figure 2 but in different scale, the state of pressure at the delivery starting shortly before the compressor stop and in a condition of minimum level of the compressor lubricant.

With reference to Figure 1, the numeral 1 indicates the lubricant monitoring system of a compressor 3 of a refrigerant circuit 2 and object of the present invention. The circuit 2 can preferably be of the refrigerator and/or heat pump type with one or more compressors, one or more stages and with sections fit to supply a single user or several users requiring different values of cooling capacity or temperature.
Figure 1 shows a principle schematic view of a single compressor refrigerating system, but the invention is not limited to this type of circuit being practicable immediately in any type of refrigeration system or other type using compressors or pumps.
The compressor 3 can be of almost any type with or without checking means of lubricating oil level and in the following it will be made reference to hermetic compressor of eccentric piston type on which many tests have been carried out and to which Figures 2 and 3 refer.
In the following the term "lubricant" will be used to indicate the lubricating oil and any other and different types of lubricants used in the compressor.
The compressor is equipped with an intake 5 for the input of compressible fluid (for example consisting of a refrigerating fluid at gaseous state such as CO₂ or of other fluid that is in gaseous phase at least in some conditions or portions of the circuit 2) and with a delivery 9 for the compressed compressible fluid outlet.
The compressor can be equipped with one or more accumulators and several other known optional elements, in particular with an internal or external by-pass 29 provided with a closing valve which can be operated by the control means (not shown) of the circuit which, as better reported below, when the compressor motor is switched off, closes the valve of this by-pass, preventing flows through it. During normal operation, the by-pass is active during start-up so allowing the compressor to start; during operation the bypass is closed.
Always during normal operation with the compressor stopped, the by-pass is open.
During oil monitoring phase and when the compressor is stopped, the by-pass is closed so allowing to evaluate the delivery pressure drop and therefore the pressure inside the compressor.
The compressor is preferably of an electric type whose electrical power is controlled, at least when switched off and on, by the circuit control means.
The refrigerant monitoring system of the compressor 3 of the refrigeration circuit 2 comprises a state detector 11 for the compressor switching on or off, or for supplying or not supplying the compressor motor. This state detector 11 may comprise a rotation detector of the motor axis (for example by inverter) or a voltage detector on the motor terminal or it may consist of the signal source, for switching on and off the compressor motor, which is provided in the circuit control means.
The system is also equipped with a pressure sensor 13 of compressible working fluid of the circuit, where said pressure sensor 13 is located at the delivery 9 of compressor 3 or immediately downstream of said delivery, the pressure sensor 13 it is therefore intended to provide an analog or digital signal representative of the pressure values of the compressible fluid outgoing the compressor delivery. Since the delivery 9 is in direct connection with the high pressure chamber of the compressor 3, lubricated by the lubricant, the pressure measured by the pressure sensor 13 at the delivery 9 corresponds to the pressure in the high pressure chamber.
The state detector 11 and the pressure sensor 13 are connected to a monitoring device 15 to provide the latter with data respectively on the operating status of the compressor 3 and on the compressible fluid pressure at the compressor delivery 9.
Many compressors and known circuits are originally provided with an own pressure detector of working fluid flowing from the delivery 9 of compressor 3 and said detector being intended, for example, to control this pressure by providing analogue or digital measurements to an electrical or electronic appliance for controlling said compressors and known circuits.
The pressure sensor 13 of the system of the invention can consist of said pressure sensor of the compressed working fluid coming out from the compressor delivery and the electrical signals, analog or digital, of said detector are sent to said monitoring device 15, being connected to the detector and acting as a pressure sensor 13; alternatively, for example, with a compressor without a compressible working fluid pressure detector at delivery or with a detector not suitable for supplying signals or data to the monitoring device 15, the inventive system provides for application at the delivery or at the compressor delivery manifold of an own and specific pressure sensor 13.
In both cases, the lubricant level or its insufficiency are estimated on the basis of the compressible fluid pressure at the compressor outlet without direct or indirect access to oil or other lubricant.
The monitoring device 15 may be an independent entity that can be connected to the circuit control means, for example for acquiring the compressor on or off status, or the monitoring device 15 can be integrated with the circuit control means.
When monitoring device 15 detects that the compressor status changes from on to off, it records the flow of the working fluid pressure at delivery 9 supplied by pressure sensor 13 or detects one or more parameters of this flow, for example TSa time, counted starting from the compressor shutdown, necessary in order that the delivery pressure value to stabilize on a nearly constant value. With a compressor equipped with a starting by-pass, in normal operating conditions, the by-pass is active only during starting to allow the compressor to start while during next operation the bypass is closed and when the compressor is stopped, the by-pass is open.
During the oil monitoring phase, that is during the detection of the working fluid pressure at the delivery, when the compressor is stopped the by-pass is closed by the system, in this way it is possible to evaluate the delivery pressure drop and then to estimate the pressure inside the compressor. This happens because the delivery gas and oil, if present, flow internally to the compressor from the delivery chamber to the intake chamber.
The behavior is different with or without oil. If gas passes between the internal seals (seals between compressor delivery and intake), then the pressure drop in the compressor delivery chamber is rapid if, on the contrary, oil passes, this drop is slow. The monitoring device 15 performs, by means of one or more algorithms stored therein, a comparison between the working pressure of the compressible working fluid at the delivery 9 starting from this detection of the stop instant and a predetermined flow memorized therein.
In the event of a discrepancy between the two flows grater than a predetermined threshold, the monitoring device 15 emits at least one low level alarm signal of the lubricating oil.
Said flow can be summarized in the TS time for stabilization of the pressure at the delivery starting from the compressor shutdown. In fact, this simple parameter has shown to be advantageously and surprisingly able to provide a reliable evaluation of the lubricating oil level of the compressor: in fact, as the quantity of lubricating oil in the compressor decreases, the time, required to pressure for stabilize itself on a value almost constant and equal to the pressure value at the intake of the compressor, is reduced.
In other words, the time interval TSa required for stabilizing said pressure in the compressor with the maximum amount of lubricant is greater than the duration of the time interval TSm required for stabilizing such pressure in the compressor with the minimum amount of lubricant (comparing TSa and TSm times in Figures 2 and 3 it can be taken into account the scale diversity of the respective abscissas axes which flattens the differences in such times and flows).
It is therefore possible to compare the duration value of TS time interval for the pressure stabilization at delivery starting from the compressor shutdown with a pre-memorized threshold value and corresponding to the minimum lubricant quantity considered acceptable; if this TS time is lower than the set threshold value, then the monitoring device 15 detects a minimum (or insufficient) lubricant condition and emits at least said low level alarm signal of oil or of other lubricant.
In other words, the monitoring device 15 compares the pressure flows by comparing the time required to the pressure of the compressible fluid at the delivery 9 to stabilize or, alternatively, to reach a predetermined standard value, with corresponding time values.
From Figure 2, it can be noted that the downward trend of pressure at the delivery after the compressor shutdown, having the maximum amount of lubricating oil, takes place (at least in many types or varieties of compressors, lubricants and in a prior detectable operating conditions) in two phases; the first phase, probably due to lubricating oil flow from the delivery 9 to the intake 5, occurs during the first time segment tl and has a low slope and a concavity which is average facing toward the abscissa axis; the second phase, probably due to the working fluid gaseous flow backwards from the delivery 9 to the intake 5, occurs during the second time segment tf and has a greater slope and a concavity facing upwards or in a direction opposite to that of the abscissas axis.
As the amount of lubricating oil decreases, the first phase is also reduced until reaching the flow of Figure 3 corresponding to the minimum amount of lubricating oil and in which the first phase has almost disappeared.
This probably occurs because the oil does not only serve as a lubricant but also as a liquid packing between the compressor active parts.
The calculation of the first and/or second derivatives (for example carried out by calculating the pressure differentials at appropriate sampling time intervals) of the time flow of pressure at the delivery after the compressor has been switched off at particular times starting from that shutdown or for all the flow makes it possible to evaluate the achievement of the minimum acceptable lubricant amount, for example a high absolute value of the first derivative shortly after the compressor switching off or a second derivative corresponding to a concavity almost always turned upwards indicate that the lubricating oil amount in the compressor is minimal or low.
It is therefore provided, alternatively or in addition to the counting and to the comparison of the pressure stabilization time TS, that the monitoring device 15 can compare the pressure flows by comparing the values of the first and/or second derivatives at certain time intervals or their average values in one or more time intervals or the integrals of such flows starting from the extinction instant until the moment in which the pressure of the compressible fluid at the delivery 9 stabilizes or reaches a predetermined value.
In order to obtain and store in the monitoring device 15 parameters and/or comparison flows therein 15 one or more predetermined reference flows of the pressure at the delivery can be stored, which can be selected according to the lubricant type and/or to the operating conditions or is memorized in the monitoring device 15 one or more real pressure flows to the delivery detected following to the compressor shutdown in real operating conditions in which the compressor contains the maximum amount of lubricating oil.
It is also provided that the monitoring device 15, following to the compressor switching off, operates each connection and by-pass closing between intake and delivery of the compressor.
The system also comprises a non-return valve 17 placed immediately downstream of the delivery 9 and assigned to prevent flows towards the delivery which could change the pressure flow measured at the delivery 9 by the pressure sensor 13.
Alternatively or added to this non-return valve, the system may comprise a closing valve of the circuit placed downstream of the delivery and actuated in closing by the control means of the circuit, or by the monitoring device 15, when the compressor is switched off.
The monitoring device 15 is preferably of microprocessor-programmable digital type and provided with input ports at least for the signals provided by the state detector 11 and by the pressure sensor 13 and with at least one output port for the alarm signal for the activation of acoustic and/or optical alarms and with an optional door for the closing command of the optional closing valve of the circuit, if provided.
The monitoring device 15 can be provided with a digital output connected to transmission means, for example of a wired local network or wireless type or of a type for remote communications, and in said alarm case (that is, a discrepancy between the two detected and reference flows, higher than a predetermined threshold) sends through said transmission means an alarm signal in digital form to at least one local or remote operating center.
The monitoring device 15 can be provided with a control output directly or indirectly connected, to electrical supply dissection means 18 of the compressor to shut off the latter in correspondence with the generation of an alarm signal regardless of the circuit control means.
In order not to interrupt the functionality of the circuit even in case of alarm and stop of the compressor, the monitoring device 15 can be provided with a control output connected, directly or indirectly, to circuit reserve compressors for the activation of the latter in correspondence with the generation of the alarm signal.
As seen and preferably, the circuit 2 and the working fluid are of refrigerating type and said circuit comprises, in addition to the compressor 3 or to the compressors and starting from the respective deliverys at least one condenser or gas cooler 21, a capillary or rolling valve 23, and an evaporator 25. The circuit may be provided with a condenser or a with gas cooler depending on the type of refrigerating fluid used, in particular, if CO₂ is used as working fluid, the circuit will be provided with a gas cooler or a CO₂ cooling exchanger, in the following the term exchanger will be used to indicate both: exchanger and gas cooler. The circuit 2 can further comprise at least one of the oil separator means 27 having an input and an output for the compressible fluid connected respectively to the delivery 9 and to the input of the condenser 21 and an output for the lubricating oil connected to the intake 5 of the compressor body 3; the circuit 2 can further comprise at least one of flow control valves, by-pass, gaseous and liquid phases separators of the working fluid, high pressure valves and flash-gas valves.
It should be noted that the present invention has shown great efficiency and functionality in systems provided with one or more completely hermetic compressors in which it is not possible to use sensors and/or to see inside and which are often without level, pressure or other lubricating oil parameter sensors. Furthermore, it is to be noted that the present invention allows the use of the working fluid pressure standard sensors of the circuit in the collector or delivery lumen of the compressor to estimate the lubricating oil level without any detection of the parameters and state of the lubricating oil itself. Finally, it should be noted that in the case of a compressor and/or system without pressure sensors of working fluid at the delivery, in general it is very easy and easy to apply a pressure sensor to the system delivery according to the invention, as opposed to the level and/or lubricating oil pressure detectors which often cannot be installed ex novo and which often, if present, are not accessible.

Claims

Monitoring system of lubricant of a compressor (3) of a refrigerant circuit (2) for a compressible fluid where the compressor is equipped with an intake (5) and a delivery (9); said monitoring system (1) comprising an on-off state detector (11) of the compressor (3), a pressure sensor (13) at the compressor delivery (9) and a monitoring device (15) connected to said on-off state detector (11) and to the pressure sensor (13) to provide the monitoring device (15) respectively with data on operating or switch-off status of compressor (3) and data flow along time on the pressure of compressible fluid at compressor delivery (9), characterized in that following the detection by the monitoring device (15) of the compressor status switching from on to off, said monitoring device (15) is configured to compare the course of the data flow along the time of the pressure values of the compressible fluid at the delivery (9), starting from the switching instant in the shutdown state, with a predetermined course memorized therein; in case of a discrepancy between the two courses exceeding a predetermined threshold, the monitoring device (15) is configured to emit at least one alarm signal where the monitoring device (15) is configured to compare the pressure courses by comparing the time needed for the pressure of the compressible fluid at delivery (9) to stabilize or to reach a predetermined value with the corresponding times which constitute the predetermined stored course; or the monitoring device (15) is configured to compare the pressure courses by comparing the values of the first and/or second derivatives at certain time intervals or their average values in one or more time intervals or integrals of the pressure course from the shutdown instant until the pressure of compressible fluid at delivery (9) stabilizes or reaches a predetermined value with corresponding predetermined values of the first and/or second derivatives , the average values or the integrals of the pressure course.
System according to claim 1 characterized in that in the monitoring device (15) one or more predetermined reference course of the delivery pressure are memorized according to the lubricant type and/or to the operating conditions or it is stored in the monitoring device (15) one or more real pressure course at delivery detected following the compressor shutdown in real operating conditions.
System according to any of the previous claims characterized in that the monitoring device (15), following the shutdown of compressor, operates the locking of each connection and by-pass between intake (5) and delivery (9) of compressor (3) and in that it comprises a non-return valve (17) located downstream of delivery (9) to prevent the refrigerating fluid flow towards the delivery itself.
System according to claim 3, characterized in that the monitoring device (15) is microprocessor-programmable digital input and has input ports at least for signals provided by the state detector (11) and the pressure sensor (13) and at least one output port for the alarm signal to activate acoustic and/or optical alarms.
System according to any of the previous claims characterized in that the monitoring device (15) is provided with a digital output, connected to transmission means and in said case with a discrepancy between two courses exceeding a predetermined threshold, sends via said transmission means an alarm signal in digital form to at least one operating station.
System according to any of the previous claims characterized in that the monitoring device (15) is provided with a control output connected, directly or indirectly, to means for disconnecting the electric power supply (18) of the compressor to shut off the latter in correspondence of alarm signal generation.
System according to any of the previous claims characterized in that the monitoring device (15) is provided with a control output connected, directly or indirectly, to backup compressors of circuit for activation of the latter in correspondence with alarm signal generation.
System according to any of the previous claims characterized in that the circuit (2) and the compressible fluid are of refrigerating type and said circuit comprises, in addition to compressor (3) and starting from its delivery (9) at least one condenser (21), a capillary or laminating valve (23), and an evaporator (25), said circuit (2) may also comprise at least one of oil separator means (27) having an inlet and an outlet for the compressible fluid connected respectively to delivery (9) and to condenser inlet (21) and to an oil outlet connected to intake (5) of compressor (3); said circuit (2) can further comprise at least one between flow control valves, by-pass, gaseous and liquid fluid phase separators, high pressure valves, flash gas valves.