DE102014019856B3 - Method and device for monitoring a fill quantity of a refrigerant - Google Patents

Abstract

The invention relates to a method and a device for monitoring a fill quantity of a refrigerant in a refrigerant circuit (46) of a refrigeration system (10), with a compressor (12), a condenser or a gas cooler (14), an expansion device (16) and an evaporator device (18). With the compressor (12) switched on, the method comprises the following steps: measuring at least one temperature of the refrigerant in the refrigerant circuit (46) at the outlet of the condenser or the gas cooler (14); Measuring a pressure of the refrigerant at the outlet of the condenser or the gas cooler (14); Determination of an underfilling of refrigerant, in particular an underfilling of refrigerant, if the measured pressure is outside a setpoint pressure range, a setpoint pressure of the refrigerant being determined based on the measured temperature, and the setpoint pressure range comprising pressure values which deviate from the setpoint pressure by at most a specified tolerance , the target pressure being the evaporation pressure of the refrigerant, or the target pressure being the evaporation pressure of the refrigerant extrapolated beyond a critical point (PC) of the refrigerant, the measured temperature being increased by a predetermined value to determine the target pressure. The device according to the invention further comprises a reservoir (22) storing a refrigerant and a refrigerant operated in the transcritical range as a function of the operating point, in particular CO2, at least one refrigerant temperature sensor (32) and at least one refrigerant pressure sensor (34) being provided for measuring the temperature and pressure of the refrigerant, wherein the temperature and pressure of the refrigerant can be evaluated in a control unit (30) in such a way that an underfilling of refrigerant can be detected, and the control unit (30) initiates filling by means of control interventions on the refrigerant circuit (46) if underfilling is detected. The refrigerant temperature sensor (32) and the refrigerant pressure sensor (34) are provided on an output side (35) of the gas cooler (14).

Description

The invention relates to a method for monitoring a refrigerant charge of a refrigerant circuit of a refrigeration system, to filling such a refrigeration system by means of a refrigerant, and to a device for monitoring a refrigerant charge of a refrigeration system, in particular for a vehicle.

Compression refrigeration systems or air conditioning systems are used, for example, for air conditioning vehicles such as passenger cars or buses as air conditioning systems in order to reduce the temperature in the interior of the vehicle. A generic compression refrigeration system comprises a refrigerant-carrying system with a condenser unit, which comprises at least one condenser or at least one gas cooler, furthermore an expansion device, an evaporator unit and a compressor, which are connected to one another via refrigerant-carrying lines. A refrigerant circulates in this closed circuit.

From the point of view of environmental compatibility, carbon dioxide (CO ₂ ) is used as an alternative medium for compression refrigeration systems. The naturally occurring carbon dioxide has a very low climate-damaging global warming potential compared to other refrigerants. A disadvantage of CO ₂ is its low critical temperature of only 31 ° C, which is why the heat release must take place above the critical pressure and without condensation / liquefaction. The critical pressure of CO ₂ is about 74 bar. In known compression refrigeration systems with CO ₂ as the refrigerant, the system filling in relation to the system volume, also referred to as the degree of filling, is between 50% and 100% of the critical density. Condensation does not occur in the high pressure part because the high pressure is above the critical pressure.

When such a compression refrigeration system is in operation, there is a relatively high operating pressure downstream of the compressor, and a relatively low pressure prevails upstream of the compressor. At standstill, pressure equalization takes place, and there is still a relatively high standstill pressure in the circuit of the compression refrigeration system. The compressor must be designed for the relatively high standstill pressure and protected accordingly. At a system temperature of 40 ° C and a filling level of around 50% of the critical density of the refrigerant carbon dioxide, the system pressure is around 75 bar, and at a filling level in the range of the critical density of the refrigerant it is around 89 bar. With a system temperature of 60 ° C and a degree of filling of 50% of the critical density of the refrigerant, the system pressure is around 89 bar and with a degree of filling of 100% of the critical density of the refrigerant, around 124 bar.

In the refrigerant circuit, it is necessary to reliably determine the fill level of the refrigerant circuit, i.e. the amount of refrigerant in the refrigerant circuit, in order to detect, in particular, an underfilling of the refrigerant. The amount of refrigerant specified for a particular air conditioning system or refrigeration system must be adhered to within very narrow tolerances, since overfilling or underfilling the system can lead to losses in refrigeration capacity and even damage to the same. In particular, underfilling can lead to unstable conditions, which can also lead to a short-term breakdown of the circuit. The degree of filling of compression refrigeration systems is generally determined in the context of idle state analyzes, with the pressure of the refrigerant being measured by means of a pressure sensor and being related to a temperature of the refrigerant.

In a further development of known compression refrigeration systems with carbon dioxide as the refrigerant, which is a non-flammable, inert, non-toxic medium and is harmless under normal conditions in a gaseous state, carbon dioxide from the compression refrigeration system can be used as an extinguishing medium in corresponding extinguishing systems of vehicles. The refrigerant CO _{2 has} proven to be a suitable fire extinguishing agent to extinguish any sources of fire that may arise and / or are caused by traffic accidents. The extinguishing medium CO ₂ shows advantages over cooling water used in a comparable way.

the end U.S. 5,481,884 A a method for standstill monitoring and also for monitoring the filling quantity during the operation of an air conditioning and heat pump system is known. While the system is in operation, the temperature and pressure of the refrigerant are measured on the suction side of the compressor. The associated saturation temperature is determined for the measured pressure and used as a reference temperature with which the measured refrigerant temperature is compared. If the measured temperature is above the reference temperature, an underfilling is concluded.

DE 100 61 545 A1 describes a method for monitoring the refrigerant charge in a refrigerant circuit of an air conditioning or heat pump system with a compressor and, depending on the operating point, refrigerants operated in the supercritical range at standstill and / or in operation. During the commissioning of the fill quantity monitoring, refrigerant overheating, ie a temperature rise at the evaporator of the system, is recorded and the recorded overheating is compared with a limit value. If the overheating exceeds a predeterminable maximum value, an underfilling is concluded and corresponding warning information is generated.

From U.S. 5,481,884 A and DE 100 61 545 A1 Known methods can in principle be applied to all refrigerants and thus also to CO ₂ , but these methods only detect faulty states of the refrigerant at the inlet of the compressor, ie on the low-pressure side. However, a faulty state can also arise, for example, from a defective expansion element or a blockage in the refrigerant circuit. Both types of error present serious dangers for the compressor.

the end DE 44 11 281 B4 an air conditioning system for a motor vehicle is known which _{uses CO 2} as a circulating medium, the circulating medium CO _{2 of} the air conditioning system being used specifically as a fire extinguishing agent in the event of a fire. In the air conditioning system, the circulating medium is circulated in pressure lines, from which fire extinguishing lines with magnetic valves arranged on them and controllable via a control unit branch off and end in extinguishing nozzles. _{The CO 2} made available to the extinguishing device generally contains a lubricant which is used in the circulating medium to lubricate the moving parts.

DE 10 2014 003 908 A1 refers to a vehicle air conditioning system with a refrigerant circuit. This comprises as components at least one evaporator, a refrigerant compressor, a refrigerant condenser, an expansion valve assigned to the evaporator and at least one heat exchanger with an assigned expansion valve provided for coupling to a coolant circuit of a heat source. The components are connected to one another by means of a refrigerant line. A refrigerant container connected to the refrigerant line on the high pressure side of the refrigerant compressor comprises a refrigerant receiving chamber with a controllable volume. Furthermore, a control unit is provided with which the volume of the chamber of the refrigerant container is controlled as a function of operating parameters of the refrigerant circuit.

KR 10 136 87 94 B1 refers to a refrigeration circuit housed in a variable volume container. The container is controllable in such a way that it takes up a volume for storing a refrigerant, based on the change in the operating conditions, for example an outside temperature or a temperature under a load. In this way, optimal operation can be achieved, regardless of a change in an outside temperature or a temperature occurring under load, by ensuring an appropriate cooling adjustment when the operating conditions change.

Disclosure of the invention

According to the invention, a method for monitoring a refrigerant charge of a refrigerant circuit of a refrigeration system and a filling of such a refrigeration system by means of a refrigerant, as well as a device for monitoring a refrigerant charge of a refrigeration system are proposed, wherein the refrigerant can be used as an extinguishing medium. In particular, the invention enables reliable monitoring during ongoing operation of the refrigeration system. The method for monitoring the refrigerant charge in the refrigerant circuit is proposed for a refrigeration system in the form of a compression refrigeration system.

A compression refrigeration system to be monitored, which is used to control the temperature of air in vehicles, comprises a refrigerant-carrying system with a condenser unit, which includes at least one condenser or at least one gas cooler, an expansion device, an evaporator unit and a compressor, which are connected to one another via refrigerant-carrying lines. A separate expansion vessel can be connected to the refrigerant circuit via a valve, the expansion vessel in particular being arranged downstream of the expansion device on the low-pressure side. To monitor the conditions within the circuit, for example, temperature sensors are required to record the temperature and the pressure. A refrigerant circulates in this closed circuit. Such a system is designed as a transcritical system, i.e. it is designed to be transcritical, with carbon dioxide being used as the refrigerant.

When the refrigerant charge in the refrigerant circuit changes, values of various parameters change at different positions in the refrigerant circuit, such parameters representing measured quantities that are sensitive to the amount of liquid. In transcritical compression refrigeration systems, a change in the refrigerant charge is related to a change in the pressure at predetermined positions in the refrigerant circuit, so that the pressure can be viewed as a charge-sensitive parameter. A change in the refrigerant temperature at predetermined positions in the refrigerant circuit is also related to a change in the refrigerant charge. A change in the subcooling of the refrigerant at the outlet of the condenser unit can also be viewed as a level-sensitive parameter. A correspondingly positioned pressure sensor is arranged in the refrigeration system to detect the pressure and a correspondingly positioned temperature sensor is arranged in the refrigeration system to detect the temperature. Following the solution proposed according to the invention, a temperature sensor can be arranged within the refrigeration system between the outlet of the condenser or the gas cooler and the inlet of the expansion element.

For a clear determination of underfilling, it is advantageous to determine the state of the filling level on the high pressure side. It is particularly advantageous if both states, ie on the high pressure side and the low pressure side, are taken into account, in particular in combination with that in FIG DE 100 61 545 A1 described procedure.

The respective values of the fill-quantity-sensitive parameters enable the refrigerant fill quantity in the refrigerant circuit to be evaluated. In order to achieve a good cooling capacity, the refrigerant charge, which can also be represented in the form of a degree of charge, should be within narrow limits. The fill level of the refrigerant is defined as the quotient of the refrigerant charge to the total volume of the system.

The fill level can be monitored when the compressor is switched off. The balanced system pressure then follows the evaporation pressure as long as the liquid refrigerant has not evaporated. The reference temperature is the lowest temperature in the system. $$\text{p}\left(\text{T}\right)={\text{p}}_{\text{crit}}\cdot {\left(\left(\text{T}/{\text{T}}_{\text{crit}}+\text{a}\right)\cdot \text{b}\right)}^{\text{c}}+\text{d}$$

If you insert the _{corresponding values for the refrigerant CO 2} , you get: $$\text{p}\left(\text{T}\right)=73.834\cdot {\left(\left(\left(\text{T}+273.15\right)/304.21-0.350042\right)\cdot 1.54159\right)}^{4.31458}-\mathrm{0.810014.}$$

T should be entered in ° C, and p is _absolute in bar.

After complete evaporation, the pressure follows the isochore corresponding to the degree of filling as the temperature rises. To do this, insert the corresponding value in the thermal equation of state. This pressure is lower than the evaporation pressure at the same temperature. Simple thermal equations of state are, for example, the von van der Waals equation and the von Redlich-Kwong equation.

The van der Waals equation is: $$\begin{array}{l}\text{p}\left(\text{T}\right)=\text{R.}*\text{T}/\left(\text{v}-\text{b}\right)-{\text{a / v}}^{\text{2}}\\ \text{with a}=27/64*{\left(\text{R.}*{\text{T}}_{\text{crit}}\right)}^2/{\text{p}}_{\text{crit}}\text{and b}=\text{R.}*{\text{T}}_{\text{crit}}/\left(\mathrm{8th}*{\text{p}}_{\text{crit}}\right)\end{array}$$

oder $$\begin{array}{l}\text{p}\left(\text{T}\right)=\left(\left(\text{T}+\mathrm{273,15}\right)*65773-12763586\right)/100000\\ {\text{mit p in bar}}_{\text{absolut}}\text{ und T in °C}\text{.}\end{array}$$

If you use the values of CO ₂ and a filling level of 260kg / m ³ , you get: $$\begin{array}{l}\text{p}\left(\text{T}\right)=189*\text{T /}\left(\left(1/260\right)-0.0009732\right)-188.81/{\left(1/260\right)}^2\\ \text{with p in Pa and T in K}\end{array}$$

or $$\begin{array}{l}\text{p}\left(\text{T}\right)=\left(\left(\text{T}+273.15\right)*65773-12763586\right)/\mathrm{100,000}\\ {\text{with p in cash}}_{\text{absolutely}}\text{and T in ° C}\text{.}\end{array}$$

The Redlich-Kwong equation is: $$\begin{array}{l}\text{p}\left(\text{T}\right)=\text{R.}*\text{T}/\left(\text{v}-\text{b}\right)-\text{a}\left(\text{T}\right)/\left({\text{v}}^{\text{2}}+\text{bv}\right)\\ \text{with a}=0.42748*{\left(\text{T}/{\text{T}}_{\text{crit}}\right)}^{-0.5}\text{*}{\left(\text{R.}*{\text{T}}_{\text{crit}}\right)}^{\text{2}}{\text{/ p}}_{\text{crit}}\text{and b}=0.08664*\text{R.}*{\text{T}}_{\text{crit}}{\text{/ p}}_{\text{crit}}\end{array}$$

oder $$\begin{array}{l}\text{p}\left(\text{T}\right)=\left(\left(\text{T}+\mathrm{273,15}\right)*59580-191916760*{\left(\text{T}+\mathrm{273,15}\right)}^{-\mathrm{0,5}}\right)/100\text{000}\\ {\text{mit in bar}}_{\text{absolut}}\text{ und T in °C}\text{.}\end{array}$$

If you use the values of CO ₂ and a filling level of 260kg / m ³ , you get: $$\begin{array}{l}\text{p}\left(\text{T}\right)=189*\text{T}/\left(\left(1/260\right)-0.00067454\right)-191.32*{\left(\text{T}/304.21\right)}^{-0.5}/\left({\left(1/260\right)}^2+0.00067454/260\right)\\ \text{with p in Pa and T in K}\end{array}$$

or $$\begin{array}{l}\text{p}\left(\text{T}\right)=\left(\left(\text{T}+273.15\right)*59580-191916760*{\left(\text{T}+273.15\right)}^{-0.5}\right)/100\text{000}\\ {\text{with in cash}}_{\text{absolutely}}\text{and T in ° C}\text{.}\end{array}$$

A temperature outside the refrigerant circuit, for example an internal temperature of the vehicle or an external temperature, can be used as the reference temperature. However, a temperature measured in the refrigerant circuit, such as an evaporator temperature measured via an icing sensor, can also be used. If several temperatures are measured, the lowest of the measured temperatures is advantageously used.

In particular, when the compressor is switched on, i.e. during operation, the charge level is monitored by means of appropriate sensor devices, with measured variables that are dependent on the refrigerant charge level being determined. Here, on the high pressure side of the refrigerant circuit, i.e. downstream of a compressor and a condenser unit, in particular a gas cooler, and upstream of an expansion device, the pressure and the temperature of the refrigerant are recorded by an appropriately positioned pressure sensor and a temperature sensor. The recorded values are evaluated in such a way that an incorrect filling is inferred if the measured pressure of the refrigerant lies outside a predetermined setpoint pressure range assigned to the recorded temperature. If the measured pressure falls below the specified setpoint pressure range or a minimum pressure that can be specified based on the setpoint pressure, which corresponds to a specified minimum density and consequently a specified minimum fill quantity of the refrigerant and is dependent on the current refrigerant temperature, an underfilling of refrigerant in the system is concluded and a corresponding signal is generated, which sets further steps in motion. For example, a warning signal is output which can be output as a service message in acoustic and / or optical form.

In a preferred embodiment, a further step of the method proposed according to the invention comprises an automatic filling of the refrigerant system with refrigerant, for example refrigerant being stored in a storage container integrated in the system and being supplied by means of a controlled metering device. The metering device includes, among other things, a controlled valve unit with a solenoid valve and a non-return valve, which are open until the pressure sensor arranged after the condenser unit or the gas cooler or condenser detects a pressure of the refrigerant that is within the setpoint pressure range that is to be detected Temperature at the output of the condenser unit-based setpoint pressure corresponds.

In the context of the invention, the term target pressure range is understood to mean that pressure range which includes pressure values that deviate from that target pressure by a maximum of a tolerance of, for example, +/- 10%, or also referred to as the limit pressure value that is determined based on the temperature by to achieve maximum efficiency. This target pressure results from an optimization of the cooling capacity in connection with a compressor shaft power. One parameter of the optimization is the refrigerant temperature at the outlet of the heat-dissipating gas cooler, whereby from the thermodynamic Data of the refrigerant used or the target pressure is determined by corresponding measurements, which is required to achieve maximum efficiency.

oder $$\text{p}\left(\text{T}\right)=74+2\cdot \left(\text{T}-31+5\right),\text{ mit p in bar und T in °C einzusetzen}\text{.}$$

A setpoint pressure of the refrigerant is approximately determined on the basis of the determined temperature at the outlet of the condenser or the gas cooler. In the simplest case, for example, this can be determined from a straight line equation or a sectional straight line equation, according to the following relationships: $$\text{p}\left(\text{T}\right)=90+2\cdot \left(\text{T}-35\right),\text{to be used with p in bar and T in ° C}\text{,}$$

or $$\text{p}\left(\text{T}\right)=74+2\cdot \left(\text{T}-31+5\right),\text{to be used with p in bar and T in ° C}\text{.}$$

At the onset of the critical pressure of 74 bar, the critical temperature of 31 ° C and an assumed subcooling of 5 ° C, slightly higher target pressures are obtained.

An alternative for determining better results is to use the vapor pressure curve and extrapolate it beyond the critical temperature, with a certain supercooling, for example of the order of 5 K, being specified. A practical relationship for vapor pressure is: $$\text{p}\left(\text{T}\right)={\text{p}}_{\text{crit}}\cdot {\left(\left({\text{T / T}}_{\text{crit}}+\text{a}\right)\cdot \text{b}\right)}^{\text{c}}+\text{d}$$

For the refrigerant CO ₂ , insert the corresponding values and get: $$\text{p}\left(\text{T}\right)=73.834\cdot {\left(\left(\left(\text{T}+273.15\right)/304.21-0.350042\right)\cdot 1.54159\right)}^{4.31458}-\mathrm{0.810014.}$$

T should be entered in ° C and p is _absolute in bar. At 5 ° C subcooling, the target pressure is: $$\text{p}\left(\text{T}\right)=73.834\times {\left(\left(\left(\text{T}+278.15\right)/304.21-0.350042\right)\cdot 1.54159\right)}^{4.31458}-\mathrm{0.810014.}$$

An exact determination of the optimal setpoint pressure would require a determination of the cooling capacity achieved and the compressor capacity used for it. However, this would require additional pressure and temperature sensors at the inlet and outlet of the compressor, which is associated with considerable additional effort. For the reasons mentioned, a simple, approximate determination using a straight line equation or using vapor pressure extrapolation is preferred in the present case. On the high pressure side of a transcritical compression refrigeration system, the vapor pressure can be extrapolated well with 5 K subcooling after the gas cooler. At a temperature of 30 ° C there is a pressure of about 80 bar, at a temperature of 35 ° C there is a pressure of about 90 bar and at a temperature of 40 ° C there is a pressure of about 100 bar.

On the basis of the determined temperature value and a limit pressure curve established in a temperature pressure diagram, the value of the setpoint pressure can be established with which the measured pressure is comparable. By comparing the measured pressure with the setpoint pressure, it is concluded that the refrigerant in the refrigerant circuit is incorrectly filled. In particular, it is possible to conclude that there is underfilling if the measured pressure lies outside a predefined setpoint pressure range, which is determined from the setpoint pressure and a predefinable tolerance for the detected temperature.

If underfilling is detected, in a compression refrigeration system that is in operation, controlled filling can take place on the suction side of the compressor from a storage container via a filling connection provided. In an alternative embodiment, the refrigerant system is filled via an external source, for example during a visit to the workshop.

The storage container integrated into the system, for example designed as a refill bottle, is in one embodiment fixedly arranged in a vehicle, for example in the trunk or in the tank of a vehicle and thus not in the area of the engine compartment, where elevated temperatures prevail. In particular, a filling connection with a solenoid valve and a check valve can be provided on the suction side of the compressor, via which a defined amount of refrigerant is introduced into the refrigerant circuit. The position of the filling connection of the storage container on the low-pressure side is before or after the evaporator device when gaseous refrigerant is supplied. However, if a liquid refrigerant is supplied, the position of the filling connection is in front of the evaporator device.

If underfilling of the refrigerant system is detected, the pressure of the refrigerant is too low and the refrigerant system is topped up with refrigerant, for example, when the compressor is switched on, topping up to a predetermined target pressure takes place.

However, it could also happen that the pressure inside the refrigerant system is so low that the compressor was switched off via the low-pressure switch. When the compression refrigeration system comes to a standstill, pressure equalization takes place between the high-pressure side and the low-pressure side of the refrigeration system, which includes the area from the expansion device, the evaporator device to the inlet of the compressor, and an equalization pressure is established in the refrigerant circuit of the system. In this case, the refrigerant system is first filled with refrigerant from the storage tank without the compressor being switched on, until the equalization pressure is reached between the system and the storage tank or until the switch-on pressure of the low-pressure switch of the compressor and further filling with the compressor switched on until the pressure is reached is within the target pressure range.

The relationship between the pressure of the refrigerant and the temperature of the refrigerant or a comparable temperature is used to evaluate the degree of filling of the refrigerant circuit in such a way that an incorrect filling quantity is determined. The assessment of the filling quantity is based on the relationship between pressure, temperature and filling quantity. The result of the evaluation of the incorrect filling quantity can be used as a triggering event for the filling of the refrigerant circuit from an integrated storage container, whereby the filling can be checked. When the compressor is switched on, the filling and thus the compensation of an incorrect filling quantity takes place via a line regulated by means of a valve unit, the filling quantity-sensitive parameters pressure and temperature being measured with the corresponding sensors. If the volume-sensitive parameters of pressure and temperature are again within the specified target pressure ranges, the supply of refrigerant from the storage container is terminated, for example by a corresponding control signal to the valve unit and any warning that may be issued. It is thus possible to adhere to a prescribed filling quantity, which is a prerequisite for the refrigeration system to have the most loss-free refrigeration capacity possible.

The storage container is connected to the refrigerant circuit, it being arranged on the low-pressure side of the compression refrigeration system on the line downstream of the evaporator device and upstream of the suction side of the compressor via the valve unit. In one embodiment, the storage container storing the refrigerant comprises a heating device in order to increase the temperature and thus also the pressure in the storage container, so that the filling process of the refrigerant system can be considerably accelerated and shortened.

Furthermore, the refrigerant stored in the storage container, in particular CO ₂ , can be used as an extinguishing medium for an extinguishing system of the vehicle. For sources of fire that may occur on a vehicle or are caused by a traffic accident, in particular in an engine compartment, _{extinguishing devices are provided which, if necessary, provide the refrigerant CO 2} as an extinguishing medium. According to the invention, this refrigerant can be stored in the storage container and be available both for filling the refrigeration system and the extinguishing devices. The extinguishing system includes extinguishing agent lines and nozzles that end at possible sources of fire in sensitive areas of the vehicle. In the event of a crash and / or fire, an automatic extinguishing process can take place via a corresponding sensor system, with the stored CO ₂ , which is in particular oil-free, displaces the atmospheric oxygen from the fire-endangered areas in such a way that a preventive measure to avoid a fire is achieved. In particular, the carbon dioxide stored in the storage container is oil-free in contrast to the refrigerant carried in the refrigerant circuit, which, due to the high solubility of the lubricating oil used in the compressor, carries oil with it on the high pressure side.

In the event of a crash and / or fire, an automatic extinguishing process is triggered, whereby the escaping refrigerant displaces the atmospheric oxygen that is involved in the development of the fire, without any additional fire-endangering oil being transported to the overheated area.

Figure list

Embodiments of the invention are explained in more detail with reference to the drawing.

• 1 ein schematisches Blockdiagramm einer Kälteanlage mit dem Kältemittel CO₂ und eine Überwachung der Kältemittelfüllmenge sowie einer Löscheinrichtung;
• 2 ein Flussdiagramm einer Überwachung der Kältemittelfüllmenge der Kälteanlage von 1 im laufenden Betrieb mit einer geregelten Befüllung,
• 3 eine graphische Darstellung des Zusammenhangs zwischen Temperatur und zugehörigem Solldruck des Kältemittels nach Austritt aus dem Gaskühler bei verschiedenen Verdampfungstemperaturen,
• 4 eine graphische Darstellung des Zusammenhangs zwischen Temperatur und Druck des Kältemittels nach Austritt aus dem Gaskühler bei einer Unterkühlung von 5 K im Vergleich zu einer über den kritischen Punkt des Kältemittels hinaus extrapolierten Dampfdruckkurve,
• 5 eine graphische Darstellung des Zusammenhangs zwischen Temperatur und Kälteleistungszahl des Kältemittels nach Austritt aus dem Gaskühler bei einer Unterkühlung von 5 K bei verschiedenen Verdampfungstemperaturen,
• 6 eine graphische Darstellung des Zusammenhangs zwischen Temperatur und Füllgrad des Kältemittels nach Austritt aus dem Gaskühler bei optimaler Kälteleistungszahl,
• 7 eine Skala eines Manometers mit Temperaturskala zur Messung von Druck und Temperatur des Kältemittels bei ausgeschaltetem Kompressor und
• 8 eine Skala eines Manometers mit Temperaturskala zur Messung von Druck und Temperatur des Kältemittels bei eingeschaltetem Kompressor.

Show it:

• 1 a schematic block diagram of a refrigeration system with the refrigerant CO ₂ and a monitoring of the refrigerant charge and an extinguishing device;
• 2 a flow chart of a monitoring of the refrigerant charge of the refrigeration system from 1 during operation with a regulated filling,
• 3 a graphical representation of the relationship between the temperature and the associated target pressure of the refrigerant after exiting the gas cooler at different evaporation temperatures,
• 4th a graphical representation of the relationship between temperature and pressure of the refrigerant after exiting the gas cooler with a subcooling of 5 K compared to a vapor pressure curve extrapolated beyond the critical point of the refrigerant,
• 5 a graphical representation of the relationship between the temperature and the refrigerant coefficient of performance after exiting the gas cooler with a subcooling of 5 K at different evaporation temperatures,
• 6th a graphical representation of the relationship between the temperature and the degree of filling of the refrigerant after it has left the gas cooler with the optimal refrigeration capacity,
• 7th a scale of a pressure gauge with a temperature scale for measuring the pressure and temperature of the refrigerant when the compressor is switched off and
• 8th a scale of a manometer with a temperature scale for measuring the pressure and temperature of the refrigerant when the compressor is switched on.

Design variants

1 shows schematically a refrigeration system 10 , which works with the refrigerant CO ₂ and can be used in a vehicle. CO ₂ is also known as carbon dioxide and as R-744. The refrigeration system 10 includes a closed refrigerant circuit 46 with a compressor 12th , a gas cooler on the high pressure side 14th is downstream. The latter is followed by a relaxation device 16 through which the circulating refrigerant is relaxed and cooled as it passes through an evaporator device 18th is supplied, which on a suction side 20th to the compressor 12th connected. The individual components 12th , 14th , 16 , 18th the refrigeration system 10 are through pressure lines 19th connected with each other.

On the suction side 20th or on the corresponding pressure line 19th between the outlet side of the evaporator device 18th and inlet or suction side 20th of the compressor 12th is a storage container 22nd connected, in which a certain amount of refrigerant is stored. The reservoir 22nd is with the pressure line 19th via a valve unit 24 connected, which includes, for example, a solenoid valve and a check valve (not shown). Furthermore, the storage container 22nd a heater 48 include, with increasing temperature the pressure of the in the storage container 22nd stored refrigerant increases, which contributes to an accelerated filling.

Via the evaporator device 18th becomes an air flow to be cooled 26th out, which is blown into an interior of a vehicle, for example. The gas cooler 14th is caused by a flow of air carried over it 28 chilled. There is also at least one control unit 30th shown showing the operation of the refrigeration system 10 controls in a conventional manner. In addition, the at least one control unit controls 30th together with detection means, a monitoring of the refrigerant fill quantity, as will be explained below.

Of the 1 it can be seen that from the at least one control unit 30th a signal to a warning device 31 can happen in the event of a detected incorrect fill level of the refrigerant in the refrigeration system 10 , with those on the warning device 31 Output information about the incorrect filling of the refrigeration system 10 informed.

The detection means comprise a refrigerant temperature sensor 32 and a refrigerant pressure sensor 34 , which on an exit side 35 of the gas cooler 14th are provided. The at least one Control unit 30th receives measurement signals from the sensors mentioned 32 , 34 and evaluates this according to a method for monitoring the refrigerant charge, this being done while the refrigeration system is in operation.

In 1 is starting from the reservoir 22nd one fire extinguisher line on behalf of several 36 shown, which end at fire-endangered locations in the engine compartment of a vehicle. At the end of the fire extinguishing line 36 is an extinguishing nozzle 38 intended. In the fire extinguishing line 36 is a solenoid valve 40 arranged via a control line 42 with the at least one control unit 30th connected is. In the at least one control unit 30th are signals from sensors 44 processed, which detect a crash and / or fire. For example, the sensors 44 Be crash sensors, which can be designed as belt tensioners and / or airbags or separate crash sensors. Alternatively or additionally, corresponding sensors can be used 44 also include temperature sensors which are arranged as fire sensors at potential fire points. Deformation sensors which can detect damage can also be included. In the event of a fire or damage caused by an accident, the at least one control unit 30th the solenoid valves 40 in the fire extinguishing lines 36 controlled, this open, so that the refrigerant CO ₂ from the storage container 22nd via the fire extinguishing lines 36 from the extinguishing nozzles 38 escapes in a controlled manner and deliberately extinguishes the source of the fire or, as a preventive measure, exposes easily inflammable areas with CO ₂ .

2 shows a flow chart of a monitoring of the refrigerant charge of the refrigeration system 10 from 1 during operation with a regulated filling.

At the start of the monitoring of the refrigerant charge in the refrigeration system 10 become the control unit 30th in a first step 100 via the one on the exit side 35 of the gas cooler 14th arranged refrigerant temperature sensor 32 the refrigerant _{temperature T KMmess and by means of the refrigerant pressure sensor} also arranged at this position 34 the refrigerant _{pressure p KMmess is} transmitted. Then in one step 102 checked that the compressor 12th the refrigeration system 10 is switched on. In the following, reference is made to the case that the compressor 12th is switched on.

Is the compressor 12th switched off, for example because the measured pressure was so low that the compressor 12th automatically switched off via a low pressure switch takes place in one step 101 a pressure equalization between the high pressure side and the low pressure side. The control unit 30th can in this case the valve unit 24 open, removing from the reservoir 22nd Refrigerant in the refrigerant circuit 46 flows in to some extent. A further filling of the refrigerant circuit 46 then continues with the compressor switched on 12th as described below.

With the compressor switched on 12th is in one step 104 _{a setpoint} pressure p _soll (T) that can be assigned to the measured temperature T KMmess is determined, with different approximations being able to be used. From the determined refrigerant temperature and the determined refrigerant pressure and on the basis of a comparison with the temperature-dependent limit pressure value or setpoint pressure, a verification of the refrigerant fill quantity is possible. The measured pressure and temperature values are compared with a limit pressure curve which reproduces the value of the limit pressure for the associated reference temperature values and is therefore used as a basis for verifying the insufficient refrigerant charge.

In one step 106 represents the control unit 30th determines whether the measured refrigerant _{pressure p KMmess lies} outside a target pressure range, which lies between a minimum pressure pmin and a maximum pressure pmax. In particular, the minimum pressure pmin is determined from the target pressure p _soll (T) and a Δp deviating from this by a tolerance, for example taking into account a tolerance of +/- 10% of the target pressure p _soll (T). The setpoint pressure p _soll (T) corresponds to a predefined minimum density of the refrigerant and thus to a predefined minimum _{fill quantity} and is dependent on the current refrigerant temperature T KMmess.

In the event that the measured pressure p _{KMmess lies} within the defined tolerance range, the monitoring process is ended. The control unit detects when the measured refrigerant _{pressure p KMmess falls below} the lower specifiable minimum pressure pmin 30th this as a refrigerant underfilling or underfilling of the refrigerant circuit 46 and generates further steps. A step 108 is the generation of a warning, which is issued in a suitable manner.

Another Step 110 refers to an automatic and controlled filling of the refrigeration system 10 with the one in the storage container 22nd stored refrigerant.

The control unit 30th opens the valve unit 24 so that on the suction side 20th of the compressor 12th via the pressure line 19th Refrigerant from the storage tank 22nd the refrigerant circuit 46 continues to be supplied until the underfilling of refrigerant in the refrigeration system 10 is balanced. The filling of the refrigeration system 10 is accompanied by a comparison of the measured refrigerant _pressure p KMmess with the setpoint pressure p _soll (T) in one step 112 . In the event that the measured refrigerant pressure in the range of the target pressure +/- a determinable tolerance, for example 2%, deviates from the target pressure, the control unit gives 30th in step 114 a signal to terminate the filling and to delete the warning.

In 3 is the relationship between the measured refrigerant _temperature T KMmess and the associated setpoint pressure p _soll (T) of the refrigerant carbon dioxide after exiting the gas cooler 14th graphically represented. One curve shows the said relationship at an evaporation temperature t0 of + 10 ° C, and the other curve shows the said relationship at an evaporation temperature t0 of -10 ° C.

The relationship between the measured refrigerant _temperature T KMmess and the pressure p of the refrigerant carbon dioxide after exiting the gas cooler 14th with a constant filling of the refrigerant circuit 46 with a subcooling of 5 K is in 4th graphically represented. For comparison, a vapor pressure curve extrapolated beyond the critical point PC of the refrigerant carbon dioxide is also drawn in the diagram.

In 5 is the relationship between the measured refrigerant _{temperature T KMmess of} the refrigerant carbon dioxide after exiting the gas cooler 14th and the coefficient of performance ε with a subcooling of 5 K is shown graphically as an example. One curve shows the said relationship at an evaporation temperature t0 of + 10 ° C, and the other curve shows the said relationship at an evaporation temperature t0 of -10 ° C.

6th shows in a graphical representation, by way of example, the relationship between the measured refrigerant _{temperature T KMmess of} the refrigerant carbon dioxide after exiting the gas cooler 14th and the fill level of the refrigerant at the optimal refrigeration capacity ε. In the example chosen, the evaporation temperature t0 is 0 ° C, the compressor 12th has an efficiency of 0.8 and the volume of the gas cooler 14th is about twice as large as the volume of the evaporator device 18th .

A scale of a manometer with a temperature scale for measuring the refrigerant _pressure p KMmess and the refrigerant _{temperature T KMmess of} the refrigerant carbon dioxide when the compressor is switched off 12th is in 7th shown as an example. In the example shown, the filling level is about 260 g / l. In this case, the refrigerant carbon dioxide is in the liquid state.

A scale of a manometer with a temperature scale for measuring the refrigerant _pressure p KMmess and the refrigerant _{temperature T KMmess of} the refrigerant carbon dioxide with the compressor switched on 12th is in 8th shown as an example. In the example shown, there is a subcooling of about 5 K. In this case, the refrigerant carbon dioxide is in a supercritical state.

The invention is not restricted to the exemplary embodiments described here and the aspects emphasized therein. Rather, a large number of modifications are possible within the range specified by the claims, which are within the scope of expert action.

Claims (14)

A method for monitoring a fill quantity of a refrigerant in a refrigerant circuit (46) of a refrigeration system (10), with a compressor (12), a condenser or a gas cooler (14), an expansion device (16) and an evaporator device (18), with a fill quantity monitoring when the compressor (12) is switched on, comprises the following steps: - measuring at least one temperature of the refrigerant in the refrigerant circuit (46) at the outlet of the condenser or the gas cooler (14); - Measuring a pressure of the refrigerant at the outlet of the condenser or the gas cooler (14); - Determination of a refrigerant underfilling, in particular an underfilling of refrigerant, if the measured pressure is outside a setpoint pressure range, a setpoint pressure of the refrigerant being determined based on the measured temperature, and the setpoint pressure range comprising pressure values which differ from the setpoint pressure by at most a specified tolerance differ, the target pressure being the evaporation pressure of the refrigerant, or the target pressure being above a critical point (PC) of the refrigerant is the extrapolated evaporation pressure of the refrigerant, the measured temperature being increased by a predetermined value to determine the setpoint pressure. Procedure according to Claim 1 , characterized in that a temperature of the refrigerant in the refrigerant circuit (46) is measured at the evaporator device (18). Method according to one of the preceding claims, characterized in that a temperature outside the refrigerant circuit (46) is measured. Method according to one of the preceding claims, characterized in that, in order to determine the setpoint pressure, the measured temperature of the refrigerant is increased by 5 ° C, or the temperature measured outside the refrigerant circuit (46) is increased by 15 ° C. Method according to one of the preceding claims, characterized in that underfilling is indicated if the pressure falls below the target pressure by more than 10 percent. Method according to one of the preceding claims, characterized in that the refrigerant is CO ₂ . Method according to one of the preceding claims, characterized in that after underfilling has been determined, the refrigerant circuit (46) is filled by means of refrigerant stored in a storage container (22) via a valve unit (24). Procedure according to Claim 7 , characterized in that the refrigerant circuit (46) is at least partially filled with the compressor (12) switched on. Method according to one of the Claims 7 until 8th , characterized in that the refrigerant circuit (46) is filled with the compressor (12) switched on and the valve unit (24) open until the measured pressure is within the target pressure range, the target pressure range comprising pressure values which are at most by a tolerance of +/- 10% deviate from the target pressure. Method according to one of the Claims 7 until 9 , characterized in that the reservoir (22) storing the refrigerant is connected to the refrigerant circuit (46) on a suction side (20) of the compressor (12). Method according to one of the Claims 7 until 10 , characterized in that the storage container (22) is tempered via a heating device (48). Device for monitoring the fill quantity of a refrigerant in a refrigerant circuit (46) of a refrigeration system (10) of a vehicle with a compressor (12), a condenser or a gas cooler (14), an expansion device (16), an evaporator device (18), a Refrigerant storing reservoir (22) and a refrigerant operated in the transcritical range as a function of the operating point, in particular CO ₂ , with a heating device (48), at least one refrigerant temperature sensor (32) and at least one refrigerant pressure sensor (34) being provided for measuring the temperature and pressure of the refrigerant, wherein the temperature and pressure of the refrigerant can be evaluated in a control unit (30) in such a way that an incorrect refrigerant charge can be detected, and the control unit (30) causes a charge to be carried out through control interventions on the refrigerant circuit (46) if underfilling is detected, characterized in that the refrigerant temperature sensor (32 ) and the Refrigerant pressure sensor (34) are provided on an output side (35) of the gas cooler (14), the refrigerant stored in the storage container (22) being used to refill the refrigerant circuit (46) of the refrigeration system (10) or to extinguish a vehicle fire. Device according to Claim 12 , characterized in that the refrigeration system (10) comprises a valve unit (24) with a solenoid valve and a check valve. Device according to one of the Claims 12 until 13th , characterized in that the storage container (22) is connected to a pressure line (19) between the outlet side of the evaporator device (18) and the suction side (20) of the compressor (12).

Images