DE102016001096B4 - Method for operating a vehicle refrigeration system, vehicle refrigeration system for carrying out the method and vehicle with such a vehicle refrigeration system - Google Patents

Abstract

Method for operating a vehicle refrigeration system with a refrigerant circuit (1), which has as components at least a refrigerant evaporator (2), a refrigerant compressor (3), a refrigerant condenser, gas cooler (4) and an expansion element (5) associated with the refrigerant evaporator (2) and electrically controllable by means of a control unit (6) with a variable valve cross-sectional area and, with a requested maximum refrigeration capacity to achieve a target air temperature (T _desired ) after the refrigerant evaporator (2), the following method steps are carried out consecutively:
a) Regulation of the valve cross-sectional area of the expansion element (5) initially to an optimum high pressure (HP _opt ) and then to a stepwise increased high pressure towards a maximum permissible high pressure (HP _perm ) at the outlet of the refrigerant condenser, gas cooler (4) until the target air temperature (T set ₎ is reached, or the high pressure is kept at the level of the maximum permissible high pressure (HP _perm ) until the target air temperature (T _target ) is reached, with the determination of the optimum high pressure (HP _opt ) based on a pressure-COP diagram depending on an ambient or outlet temperature of the refrigerant at the outlet of the refrigerant condenser, gas cooler (4), or according to the calculation rule HD _opt = T _KM × 2 + 20 with T _KM as the outlet temperature of the refrigerant at the refrigerant condenser, gas cooler (4),
b) Regulation of the valve cross-sectional area of the expansion element (5) to the last regulated high-pressure value at the outlet of the refrigerant condenser, gas cooler (4) and control of the refrigerant compressor (3) from a current delivery rate delivered at the last adjusted high-pressure value to a reduced delivery rate, as long as the target air temperature (T _set ) is maintained, and
c) Regulation of the valve cross-sectional area of the expansion element (5) in the direction of the optimum high pressure (HP _opt ) at the outlet of the refrigerant condenser, gas cooler (4) by either increasing the valve cross-sectional area as long as the temperature after the refrigerant evaporator (2) corresponds to or falls below the target air temperature (T _set ) or reducing the valve cross-sectional area as long as the temperature after the refrigerant evaporator (2) exceeds the target air temperature (T _set ).

Description

The invention relates to a method for operating a vehicle refrigeration system. Furthermore, the invention relates to a vehicle refrigeration system for carrying out the method according to the invention and a vehicle with such a vehicle refrigeration system.

Vehicle air conditioning systems are known from the prior art and are used to supply the interior or the passenger cell of a vehicle with an intake air flow at a predetermined temperature. The air conditioning unit of such a vehicle air conditioning system represents the actual ventilation system of the passenger compartment and includes an intake duct equipped with a fan, via which air, e.g. fresh air from outside the vehicle sucked in via an evaporator and/or a heating heat exchanger by means of the fan, is fed into the passenger compartment.

Such a vehicle air conditioning system is regulated by a climate control unit, which controls the components of the vehicle air conditioning system depending on predetermined operating parameters, such as the setpoint temperature set by a vehicle occupant via an operating element and the actual value of the temperature of the passenger compartment.

In today's vehicle refrigeration systems as a subgroup of vehicle air conditioning systems, expansion devices or expansion valves are used, which are predominantly mechanically adjusted or regulated. This applies in particular to the expansion devices of the interior evaporator, which are designed as fixed throttles with a fixed flow opening, fixed throttles with a bypass, which opens to absorb pressure peaks depending on the absolute value of the high pressure, or as TXV (thermal expansion devices).

A vehicle air conditioning system with a refrigerant circuit, the components of which are at least one evaporator, a controllable refrigerant compressor with variable displacement, a refrigerant condenser or refrigerant gas cooler and an electrical expansion valve with a variable valve opening that is assigned to the evaporator and can be controlled electrically by means of a control unit DE 199 17 048 A1 known. In this transcritical refrigerant circuit designed as an R744 (CO ₂ ) circuit, the refrigerant delivery capacity of the refrigerant compressor is monitored and the high pressure at the outlet of the heat exchanger is controlled by varying the opening of the expansion valve depending on the refrigerant temperature on the outlet side of the refrigerant condenser or gas cooler.

With such an externally controllable electrical expansion element for an R744 refrigeration system, the operating points of a vehicle air conditioning system can be set in such a way that the refrigerant circuit is operated at the optimum level for all operating points.

In vehicle refrigeration systems with high ambient temperatures and long vehicle downtimes, rapid cooling with maximum cooling capacity of the vehicle interior should be achieved, whereby in such situations the refrigerant pressure of R744 can increase to very high values depending on the ambient temperature.

That's it DE 10 2008 014 196 A1 discloses a method for controlling a vehicle refrigeration system using R744 as the refrigerant. This vehicle refrigeration system includes a compressor, a gas cooler, an expansion element that limits the pressure on the high-pressure side to a maximum permissible pressure, an evaporator and a blower, which supplies a temperature-controlled air mass flow to the interior via the evaporator. In this known method, the air mass flow flowing through the evaporator is reduced, for example to 10% of the maximum air mass flow, when the vehicle is restarted and when maximum cooling capacity is required. In a subsequent step, the air mass flow is kept constant until the pressure on the high-pressure side is below the maximum permissible pressure and/or the compressor is activated to the maximum. The air mass flow is then increased until the pressure on the high-pressure side has reached the maximum permissible pressure again. The sequence of steps “keeping the air mass flow constant until the pressure on the high-pressure side falls below the maximum permissible pressure” and “increasing the air mass flow until the pressure on the high-pressure side has reached the maximum permissible pressure” is repeated several times. The regulation with regard to the gradual increase in the air mass flow is terminated when the maximum air mass flow through the evaporator is reached and is taken over by the conventional series control of the refrigeration system.

Such a control of the air mass flow according to the DE 10 2008 014 196 A1 enables the use of a differential pressure-controlled expansion device in the refrigerant circuit. Furthermore, a rapid cooling of the vehicle interior is to be achieved with this known method.

The procedure according to DE 10 2004 005 175 A1 aims to prevent impermissibly high pressure peaks in an R744 refrigerant circuit. To do this, go to the pressure control a target value for an evaporator temperature is specified, from which a target value for the high pressure is derived from a basic characteristic curve by means of an evaporator temperature controller and, if necessary, modified by a correction characteristic curve. The setpoint value obtained for the high pressure is supplied to a high-pressure controller, which uses it to determine a first manipulated variable and a second manipulated variable in an additional control loop for high-pressure limitation.

Also the EP 1 955 880 A1 describes a control concept for a refrigerant circuit, which reacts quickly when a safety-relevant operating parameter, such as high pressure, is exceeded. Such a refrigerant circuit includes an evaporator temperature controller, which on the input side receives the difference between the actual value of the air temperature at the evaporator of the refrigerant circuit and a specifiable setpoint and, depending on the size of this difference, controls the compressor of the refrigerant circuit to change the pressure of the compressed refrigerant.

The known method according to this EP 1 955 880 A1 is that if a limit value for the high pressure is exceeded, the control difference is influenced in such a way that the compressor output is reduced. Thus, if the limit value is exceeded, the refrigerant circuit is no longer regulated with regard to the evaporator temperature, but rather to the safety-relevant operating parameter, namely the high pressure. If the safety-relevant operating parameter leaves the critical range again, according to this known method it is possible to switch back to the evaporator temperature control gradually or abruptly.

Furthermore, also describes the DE 10 2008 033 854 A1 an R744 refrigerant circuit, which includes an evaporator with an upstream controllable expansion valve, with which the refrigerant pressure on the high pressure side can be regulated to a predetermined target high pressure, at which the refrigerant circuit should work as efficiently as possible.

Finally, still on the DE 10 2004 029 166 A1 pointed out, which describes a method for controlling an R744 refrigerant circuit, which is intended to enable the best possible interior air conditioning even with driving situation-related limitations of the load torque of a refrigerant compressor.

In this known method according to DE 10 2004 029 166 A1 a compressor is controlled by an evaporator temperature control and a load torque limit function integrated into the same. Thus, by limiting the torque of the refrigerant compressor as a function of the driving situation, instead of switching it off, a sufficiently good air conditioning of the interior is achieved even when the vehicle engine is heavily loaded.

The object of the invention is to specify an improved method for controlling an electrical expansion element of a vehicle refrigeration system, with which on the one hand an effective operation of the refrigeration system and on the other hand rapid cooling when maximum cooling capacity is required, especially at high ambient temperatures, is achieved.

This object is achieved by a method having the features of patent claim 1 and the features of patent claim 2.

1. a) Regelung der Ventil-Querschnittsfläche des Expansionsorgans zunächst auf einen optimalen Hochdruck und anschließend auf einen schrittweise in Richtung auf einen maximal zulässigen Hochdruck am Ausgang des Kältemittelkondensators, Gaskühlers erhöhten Hochdruck, bis die Ziellufttemperatur erreicht wird, oder der Hochdruck auf dem Niveau des maximal zulässigen Hochdruckes solange gehalten wird, bis die Ziellufttemperatur erreicht wird, wobei die Bestimmung des optimalen Hochdrucks HD_opt anhand eines Druck-COP-Diagramms in Abhängigkeit einer Umgebungs- oder Austrittstemperatur des Kältemittels am Austritt des Kältemittelkondensators, Gaskühlers, oder gemäß der Berechnungsvorschrift HD_opt = T_KM × 2 + 20 mit T_KM als Austrittstemperatur des Kältemittels am Kältemittelkondensator, Gaskühlers erfolgt,
2. b) Regelung der Ventil-Querschnittsfläche des Expansionsorgans auf den zuletzt eingeregelten Hochdruckwert am Ausgang des Kältemittelkondensators, Gaskühlers und Steuerung des Kältemittelverdichters von einer bei dem zuletzt eingeregelten Hochdruckwert geförderten aktuellen Fördermenge auf eine reduzierte Fördermenge, solange die Ziellufttemperatur eingehalten wird, und
3. c) Regelung der Ventil-Querschnittsfläche des Expansionsorgans in Richtung auf den optimalen Hochdruck am Ausgang des Kältemittelkondensators, Gaskühlers, indem entweder die Ventil-Querschnittsfläche erhöht wird, solange die Temperatur nach dem Kältemittelverdampfer der Ziellufttemperatur entspricht oder diese unterschreitet, oder die Ventil-Querschnittsfläche reduziert wird, solange die Temperatur nach dem Kältemittelverdampfer die Ziellufttemperatur überschreitet.

Such a method for operating a vehicle refrigeration system with a refrigerant circuit, which has as components at least one refrigerant evaporator, one refrigerant compressor, one refrigerant condenser, gas cooler and an expansion element associated with the refrigerant evaporator and electrically controllable by means of a control unit with a variable valve cross-sectional area, is characterized according to the first-mentioned solution in that the following method steps are carried out in succession at a required maximum refrigeration capacity to achieve a target air temperature after the refrigerant evaporator:

1. a) Control of the valve cross-sectional area of the expansion device first to an optimal high pressure and then to a stepwise increased high pressure towards a maximum permissible high pressure at the outlet of the refrigerant condenser, gas cooler, until the target air temperature is reached, or the high pressure is kept at the level of the maximum permissible high pressure until the target air temperature is reached, with the determination of the optimal high pressure HD _opt based on a pressure-COP diagram depending on an ambient or outlet temperature of the refrigerant at the outlet of the refrigerant condenser, gas cooler, or according to the calculation rule HD _opt = T _KM × 2 + 20 with T _KM as the outlet temperature of the refrigerant at the refrigerant condenser, gas cooler,
2. b) Regulation of the valve cross-sectional area of the expansion element to the last regulated high-pressure value at the outlet of the refrigerant condenser, gas cooler and control of the refrigerant compressor from a high pressure value that was fed at the last regulated high-pressure value ten current flow rate to a reduced flow rate as long as the target air temperature is maintained, and
3. c) Control of the valve cross-sectional area of the expansion device towards the optimum high pressure at the outlet of the refrigerant condenser, gas cooler, by either increasing the valve cross-sectional area as long as the temperature after the refrigerant evaporator is equal to or below the target air temperature, or reducing the valve cross-sectional area as long as the temperature after the refrigerant evaporator exceeds the target air temperature.

In the second-mentioned case, this causes the high pressure to rise and thus, as a rule, the optimal high pressure to be exceeded in order to be able to set a desired blow-out temperature.

Due to the pressure losses occurring in the system, the maximum permissible high pressure after the gas cooler is primarily capped or limited in advance by the maximum permissible high pressure after the refrigerant compressor.

Alternatively, instead of referencing a directly measured air temperature downstream of the refrigerant evaporator, an indirect method linked to the low pressure can also be used to set a target air temperature.

Ideally, the evaporation pressure of the refrigerant is linked to an evaporation temperature, which in turn sets a corresponding air temperature.

1. a) Einstellung der Ventil-Querschnittsfläche des Expansionsorgans auf einen definierten Startquerschnitt und anschließend auf einen schrittweise in Richtung auf einen maximal zulässigen Hochdruck am Ausgang des Kältemittelkondensators, Gaskühlers erhöhten Hochdruck, bis die Ziellufttemperatur erreicht wird, oder der Hochdruck auf dem Niveau des maximal zulässigen Hochdruckes solange gehalten wird, bis die Ziellufttemperatur erreicht wird,
2. b) Regelung der Ventil-Querschnittsfläche des Expansionsorgans auf den zuletzt eingeregelten Hochdruckwert am Ausgang des Kältemittelkondensators, Gaskühlers und Steuerung des Kältemittelverdichters von einer bei dem zuletzt eingeregelten Hochdruckwert geförderten aktuellen Fördermenge auf eine reduzierte Fördermenge, solange die Ziellufttemperatur eingehalten wird,
3. c) Regelung der Ventil-Querschnittsfläche des Expansionsorgans in Richtung auf einen optimalen Hochdruck am Ausgang des Kältemittelkondensators, Gaskühlers, indem entweder die Ventil-Querschnittsfläche erhöht wird, solange die Temperatur nach dem Kältemittelverdampfer der Ziellufttemperatur entspricht oder diese unterschreitet, oder die Ventil-Querschnittsfläche reduziert wird, solange die Temperatur nach dem Kältemittelverdampfer die Ziellufttemperatur überschreitet, wobei die Bestimmung des optimalen Hochdrucks HD_opt anhand eines Druck-COP-Diagramms in Abhängigkeit einer Umgebungs- oder Austrittstemperatur des Kältemittels am Austritt des Kältemittelkondensators, Gaskühlers, oder gemäß der Berechnungsvorschrift HD_opt = T_KM × 2 + 20 mit T_KM als Austrittstemperatur des Kältemittels am Kältemittelkondensator, Gaskühlers erfolgt.

The method according to the second solution is characterized in that the following method steps are carried out in succession after the refrigerant evaporator when a maximum cooling capacity is requested in order to achieve a target air temperature:

1. a) Adjustment of the valve cross-sectional area of the expansion device to a defined starting cross-section and then to a stepwise increased high pressure towards a maximum permissible high pressure at the outlet of the refrigerant condenser, gas cooler until the target air temperature is reached, or the high pressure is kept at the level of the maximum permissible high pressure until the target air temperature is reached,
2. b) Regulation of the valve cross-sectional area of the expansion element to the last regulated high-pressure value at the outlet of the refrigerant condenser, gas cooler and control of the refrigerant compressor from a current delivery rate delivered at the last adjusted high-pressure value to a reduced delivery rate, as long as the target air temperature is maintained,
3. c) Regulation of the valve cross-sectional area of the expansion device in the direction of an optimal high pressure at the outlet of the refrigerant condenser, gas cooler, by either increasing the valve cross-sectional area as long as the temperature after the refrigerant evaporator corresponds to or falls below the target air temperature, or reducing the valve cross-sectional area as long as the temperature after the refrigerant evaporator exceeds the target air temperature, with the determination of the optimal high pressure HD _opt using a pressure-COP diagram depending on an ambient or outlet temperature of the refrigerant s at the outlet of the refrigerant condenser, gas cooler, or according to the calculation rule HD _opt = T _KM × 2 + 20 with T _KM as the outlet temperature of the refrigerant at the refrigerant condenser, gas cooler.

In the second case, this results in an increase in the high pressure and thus, as a rule, in the optimum high pressure being exceeded in order to be able to set a desired blow-out temperature.

These methods according to the invention are characterized by a 2-stage control strategy. In a first stage, the vehicle refrigeration system is operated at maximum power. This means that in cooling operation with maximum refrigeration capacity after the system has started up and the required boundary conditions have been reached, the cross section of the electrical expansion device is throttled so far that the maximum and permanently possible system working pressure is set at the outlet of the refrigerant condenser or gas cooler, which corresponds to the maximum permissible working pressure, hereinafter referred to as the maximum permissible high pressure, which is set at the outlet of the refrigerant compressor. Therefore, parallel to this, the pressure at the outlet of the refrigerant compressor must always be monitored, which indicates the working pressure limits of the system. This refrigeration system is thus operated at the maximum pressure ratio of high pressure to low pressure, so that the low pressure and the resulting target air temperature required and set for cooling operation with maximum refrigerating capacity is reached after the refrigerant evaporator in the shortest possible time.

The second stage of the control strategy according to the invention begins when the target air temperature is reached. Reaching the target air temperature usually means that the refrigerant compressor is no longer being operated at the delivery rate that is possible for the working point that has then been reached is controlled by a controller of a climate control unit while maintaining the target air temperature to a lower flow rate. This is equivalent to a stroke reduction or lowering of the operating speed of the refrigerant compressor.

In this operating state of the refrigerant compressor, the third stage of the control strategy according to the invention can be initiated by gradually increasing the valve cross-sectional area in order to set the optimum high pressure at the outlet of the refrigerant condenser or gas cooler, which is usually well below the maximum and permanently possible high pressure at the outlet of the refrigerant compressor or at the outlet of the refrigerant condenser or gas cooler. The gradual reduction of the high pressure at the outlet of the refrigerant condenser or gas cooler, and thus of the entire system, is carried out until the optimal high pressure is reached. According to the training, the vehicle refrigeration system is then operated at optimum high pressure in system operation and at the same time the required target air temperature is met by appropriate regulation of the refrigerant compressor.

Thus, in the third stage of the method according to the invention, the system operation of the vehicle refrigeration system leading to the target air temperature is converted with maximum and permanently possible high pressure in a gradual approximation to an effect-optimized system operation.

In this context, efficiency-optimized operation means that the vehicle refrigeration system is to be set via said expansion element to a value taken from a characteristic curve of a COP diagram for the high pressure to be controlled at the outlet of the condenser or gas cooler, with the characteristics of the COP diagram recorded as a function of the refrigerant temperature at the outlet of the condenser or gas cooler, which corresponds directly to the ambient temperature in the case of ideal heat transfer (cf. 3 ) or their mapping rules are stored in a control unit of the vehicle refrigeration system. From this COP chart after 3 it can be seen that the characteristic curves as efficiency curves are very flat at high ambient temperatures and thus outlet temperatures of the refrigerant at the refrigerant condenser or gas cooler, for example greater than 35 °C. Therefore, in the method according to the invention with performance-optimized operation compared to effect-optimized operation there are only minor losses, which can essentially be ignored.

The maximum permissible high pressure is monitored as the maximum permissible system operating pressure of the refrigeration system or heat pump at the outlet of the refrigerant compressor and the non-exceeding of this maximum permissible system operating pressure is effected by regulating the valve cross-sectional area of the expansion device, but also, if necessary, by reducing the flow rate of the refrigerant compressor by controlling it accordingly.

The method according to the invention is suitable for implementation in a vehicle refrigeration system or a vehicle air conditioning system. Such a vehicle refrigeration system or vehicle air conditioning system can be used in all vehicle types.

• - Der Kältemittelkreislauf ist auf eine maximale Leistung im Kühlungsbetrieb mit maximaler Kälteleistung ausgerichtet.
• - Bei Erreichen der Ziellufttemperatur nach dem Kältemittelverdampfer wird der Betrieb des Kältemittelkreislaufs auf einen wirkungsoptimierten Betrieb umgestellt.
• - Es wird ein beschleunigtes Erreichen eines Komforttemperaturniveaus für die Fahrzeuginsassen erreicht.
• - Der Abkühlkurvenverlauf verläuft steiler als im Stand der Technik, so dass die kälteren Temperaturen in kürzerer Zeit erreicht werden.
• - Der wirkungsoptimierte Betrieb schließt sich nach Erreichen des Komfortniveaus nahtlos an bzw. der Übergang zu diesem erfolgt unmittelbar nach Erreichen der Ziellufttemperatur.
• - Das Potenzial eines elektrischen Expansionsorgans wird maximal ausgeschöpft und damit optimal genutzt.
• - Bei Hochlast kommt es in dem leistungsoptimierten Betrieb der ersten Regelstufe des erfindungsgemäßen Verfahrens gegenüber dem anschließenden wirkungsoptimierten Betrieb nur zu geringen Einbußen, da der Effizienzkurvenverlauf gemäß den COP-Kurven (vgl. 3) bei hohen Temperaturen sich sehr flach darstellt und daher diese Verluste fast zu vernachlässigen sind.

The method according to the invention has the following advantages:

• - The refrigerant circuit is designed for maximum performance in cooling mode with maximum cooling capacity.
• - When the target air temperature after the refrigerant evaporator is reached, the operation of the refrigerant circuit is switched to an effect-optimized operation.
• - Accelerated reaching of a comfort temperature level for the vehicle occupants is achieved.
• - The course of the cooling curve is steeper than in the prior art, so that the colder temperatures are reached in a shorter time.
• - Effect-optimized operation follows seamlessly after the comfort level has been reached or the transition to this takes place immediately after the target air temperature has been reached.
• - The potential of an electrical expansion device is fully exploited and thus optimally used.
• - At high load, there are only minor losses in the power-optimized operation of the first control stage of the method according to the invention compared to the subsequent effect-optimized operation, since the course of the efficiency curve according to the COP curves (cf. 3 ) is very flat at high temperatures and these losses are therefore almost negligible.

• 1 ein Schaltbild einer Fahrzeug-Kälteanlage zur Durchführung des erfindungsgemäßen Verfahrens,
• 2 ein Ablaufdiagramm zur Erläuterung des erfindungsgemäßen Verfahrens, und
• 3 ein Druck-COP-Diagramm mit COP-Kennlinien bei überkritischem Betrieb einer R744-Kälteanlage.

The invention is described in detail below using an exemplary embodiment with reference to the accompanying figures. Show it:

• 1 a circuit diagram of a vehicle refrigeration system for carrying out the method according to the invention,
• 2 a flowchart to explain the method according to the invention, and
• 3 a pressure-COP diagram with COP characteristics for supercritical operation of an R744 refrigeration system.

The 1 shows a refrigerant circuit 1 of a vehicle refrigeration system, which consists of a refrigerant evaporator 2, a refrigerant compressor 3, a refrigerant condenser or gas cooler 4, an expansion element 5 connected upstream of the refrigerant evaporator 2 in the direction of flow of an R744 refrigerant, a heat exchanger 7 within the circuit process, and a refrigerant collector 8.

In the refrigerant circuit 1 according to 1 the expansion element 5 connected upstream of the refrigerant evaporator 2 is designed as an electric expansion valve with a variable valve cross-sectional area, which is controlled by a control unit 6 .

The electrical expansion element 5 is controlled and regulated by the control unit 6 as a function of pressure and temperature values, these pressure and temperature values being recorded by pressure-temperature sensors pT1, pT2 and pT3 and the actual value of the valve opening cross-section being transmitted to the control unit 6. The pressure-temperature sensor pT1 is arranged on the high-pressure side in the flow direction of the refrigerant after the refrigerant compressor 3, the pressure-temperature sensor pT2 in the flow direction of the refrigerant after the refrigerant condenser or gas cooler 4 and the pressure-temperature sensor pT3 in the flow direction of the refrigerant after the refrigerant collector 8 in the refrigerant circuit 1. The ambient temperature is detected by a temperature sensor T_Um and is also supplied to control unit 6 .

In the refrigeration system operation of the refrigerant circuit 1 of 1 the refrigerant compressed by the refrigerant compressor 3 is fed via the refrigerant condenser or gas cooler 4 arranged in the front area of the vehicle, where the refrigerant condenses or cools down before it is expanded into the refrigerant evaporator 2 by means of the expansion element 5 after being passed through the heat exchanger 7 within the circuit process. A flow of fresh air, circulating air or partial circulating air supplied to the refrigerant evaporator 2 is cooled by the same and supplied to a passenger compartment of the vehicle as an inlet air flow. The refrigerant evaporated in the refrigerant evaporator 2 is fed back to the refrigerant compressor 3 via the refrigerant collector 8 and the heat exchanger 7 within the cycle on the low-pressure side.

The refrigerant compressor 3 of the refrigerant circuit 1 is designed either as a mechanical refrigerant compressor or as an electrical refrigerant compressor. A mechanical refrigerant compressor is driven via a belt drive connected to the traction motor of the vehicle and is regulated by means of a control current for a compressor control valve of the refrigerant compressor in terms of differential pressure, mass flow or suction pressure. An electric refrigerant compressor has an internal electric motor as a drive, so that speed control is possible. In addition, mechanical refrigerant compressors can also be used via an electrically driven belt drive that can be decoupled from the engine.

If the control unit 6 receives a request to generate a maximum cooling capacity to achieve a target air temperature T _set after the refrigerant evaporator 2, this is based on 2 explained method according to the invention carried out by controlling the expansion element 5 by means of the control unit 6.

After the start of the method, a check is carried out in a first method step S1 to determine whether maximum refrigerating capacity is required. If such a maximum refrigeration capacity requirement exists, the high pressure at the outlet of the refrigerant condenser or gas cooler 4 is adjusted to a maximum permissible high pressure HD as the maximum working pressure of the vehicle refrigeration system using the expansion element 5 in a subsequent method step S2.

This takes place in two steps, in that first the valve cross-sectional area of the expansion element 5 is regulated to an optimal high pressure HD _opt .

Starting from the optimum high pressure HD _opt , the maximum permissible high pressure HD for the outlet of the refrigerant condenser or gas cooler 4 is then approached in a second step by adjusting the cross section of the expansion element 5, in that the target pressure is increased step by step in the direction of the maximum permissible high pressure at the outlet of the refrigerant condenser or gas cooler 4 until the target air temperature T target _is reached or the high pressure is kept at the level of the maximum permissible high pressure HD until the target air temperature T target _is reached.

According to method step S2, the valve cross-sectional area of the expansion element 5 is reduced in such a way that at the outlet of the refrigerant condenser or gas cooler 4 a high pressure that is only slightly below the system high pressure limit HD _max (= maximum permanent system operating pressure) is set. If this system high-pressure limit were 130 bar, the possible pressure losses from the outlet are taken into account of the refrigerant compressor 3 up to the outlet of the refrigerant condenser or gas cooler 4, depending on the load, about 5 bar, so that a value for the maximum permissible high pressure HD _perm of 125 bar results at the outlet of the refrigerant condenser or gas cooler 4. The maximum high pressure HP _max can be monitored directly as the system operating pressure using the pressure-temperature sensor pT1, and an optimum high pressure HP _opt can be monitored using the pressure-temperature sensor pT2.

Possible pressure losses are recorded directly using the measured values. If the pressure-temperature sensor pT2 is to be dispensed with and only the temperature at the outlet of the refrigerant condenser or gas cooler 4 is to be detected, a characteristic curve or map must be stored in the control unit 6 which, depending on the load, indicates the pressure loss across the refrigerant condenser or gas cooler 4 in order specifically to set the optimal high pressure after the refrigerant condenser or the gas cooler 4.

The optimum high pressure HD _opt is calculated using a family of characteristics of a pressure-COP diagram stored in control unit 6 3 determined as a function of an ambient temperature or the outlet temperature of the refrigerant at the outlet of the refrigerant condenser or gas cooler 4 .

This diagram shows an example of the course of COP curves depending on the ambient or refrigerant temperature in supercritical operation of an R744 refrigeration system, as is the case, for example, in 1 is shown. Thus, curve K1 shows the profile at 33°C, curve K2 the profile at 38°C, curve K3 the profile at 43°C and curve K4 the profile at 46°C.

wobei HD_opt den Wert des optimalen Hochdrucks, ermittelt aus der doppelten Austrittstemperatur T_KM des Kältemittels am Kältemittelkondensator oder Gaskühler 4 addiert mit 20, ergibt.As an alternative to the characteristic map, a calculation rule can be used. For example, the following empirical connection is known: $${\text{HD}}_{\text{opt}}={\text{T}}_{\text{KM}}\times 2+\mathrm{20,}$$

where HD _opt is the value of the optimum high pressure, determined from double the outlet temperature T _KM of the refrigerant at the refrigerant condenser or gas cooler 4 plus 20.

With method step S2, the refrigerant circuit 1 is operated starting from an initially set optimal high pressure HD _opt at the maximum pressure ratio of high pressure to low pressure along the system high pressure limit, so that the low pressure and the target air temperature T _desired resulting from it are reached early after the refrigerant evaporator 2.

Instead of method step S2, method step S2' can also be carried out. After this, the expansion element 5 is controlled with a defined starting cross-section and, based on this, regulated to the maximum permissible high pressure HD _perm at the outlet of the refrigerant condenser or gas cooler 4 by gradually increasing the target pressure in the direction of the maximum permissible high pressure at the outlet of the refrigerant condenser or gas cooler 4 until the target air temperature T target _is reached or the high pressure is kept at the level of the maximum permissible high pressure HD _perm until the target air temperature T _target is reached.

As a rule, when the target air temperature T desired is reached, the compressor speed _is reduced in electric refrigerant compressors and the control current is reduced in mechanical refrigerant compressors with mass flow control or differential pressure control. Therefore, when the target air temperature T target _is reached, according to the next method step S3, the valve cross-sectional area of the expansion element 5 is regulated to the last adjusted high pressure value at the outlet of the refrigerant condenser or gas cooler 4 and the refrigerant compressor 3 is controlled from a current delivery rate delivered at the last adjusted high pressure value to a reduced delivery rate, as long as the target air temperature T _desired is maintained.

With the reduced delivery volume of the refrigerant compressor 3 and the maintained target air temperature T set , the valve cross-sectional area of the expansion element 5 _is regulated in the subsequent method step S4 in the direction of the optimum high pressure HD _opt at the outlet of the refrigerant condenser or gas cooler 4 such that, depending on the temperature at the outlet of the gas cooler 4, a 3 optimal high pressure HD _opt sets in, which is usually significantly below the permanent pressure operating limits. A target pressure value of 106 bar would result for a coolant temperature of, for example, 43° C. after the gas cooler 4 . This regulation takes place in such a way that the valve cross-sectional area is either gradually increased as long as the temperature after the refrigerant evaporator 2 _corresponds to the target air temperature T set or falls below it or is reduced as long as the temperature after the refrigerant evaporator 2 _exceeds the target air temperature T set.

This means that the optimal high pressure HD _opt is approached step by step, starting from the higher high pressure that was last set at the outlet of the refrigerant condenser or gas cooler 4 . It should be noted that the valve cross-sectional area of the expansion device 5, taking into account the target outlet temperature Air after the refrigerant evaporator 2 can only be gradually increased as long as there is a speed or control current reserve of the refrigerant compressor 3 up to a maximum flow rate. Only then is a further enlargement of the valve cross-sectional area possible.

When the optimum high pressure HD _{opt is} reached while the target air temperature T target is maintained, according to method step S4, the transition to system operation of the vehicle refrigeration system with optimum high pressure HD _opt at the outlet of the refrigerant condenser or gas cooler 4 according to the characteristic curves takes place in a last method step S5 3 .

If no cooling operation with maximum cooling capacity is requested after method step S1, according to method step S6 the expansion element 5 is adjusted from the start to an optimum high pressure HD _opt according to the COP characteristics 3 regulated.

• - Der Kältemittelkreislauf ist auf eine maximale Leistung im Kühlungsbetrieb mit maximaler Kälteleistung ausgerichtet.
• - Bei Erreichen der Ziellufttemperatur nach dem Kältemittelverdampfer 2 wird der Betrieb des Kältemittelkreislaufs auf einen wirkungsoptimierten Betrieb umgestellt.
• - Es wird ein beschleunigtes Erreichen eines Komforttemperaturniveaus für die Fahrzeuginsassen erreicht.
• - Der Abkühlkurvenverlauf verläuft steiler als im Stand der Technik, so dass die kälteren Temperaturen in kürzerer Zeit erreicht werden.
• - Der wirkungsoptimierte Betrieb schließt sich nach Erreichen des Komfortniveaus nahtlos an bzw. der Übergang zu diesem erfolgt unmittelbar nach Erreichen der Ziellufttemperatur.
• - Das Potenzial eines elektrischen. Expansionsorgans wird maximal ausgeschöpft und damit optimal genutzt.
• - Bei Hochlast kommt es in dem leistungsoptimierten Betrieb der ersten Regelstufe des erfindungsgemäßen Verfahrens gegenüber dem anschließenden wirkungsoptimierten Betrieb nur zu geringen Einbußen, da der Effizienz-kurvenverlauf gemäß den COP-Kurven (vgl. 3) bei hohen Temperaturen sich sehr flach darstellt und daher diese Verluste fast zu vernachlässigen sind.

The method according to the invention has the following advantages:

• - The refrigerant circuit is designed for maximum performance in cooling mode with maximum cooling capacity.
• - When the target air temperature after the refrigerant evaporator 2 is reached, the operation of the refrigerant circuit is switched to an operation optimized for effect.
• - Accelerated reaching of a comfort temperature level for the vehicle occupants is achieved.
• - The course of the cooling curve is steeper than in the prior art, so that the colder temperatures are reached in a shorter time.
• - Effect-optimized operation follows seamlessly after the comfort level has been reached or the transition to this takes place immediately after the target air temperature has been reached.
• - The potential of an electric. expansion organ is used to the maximum and thus optimally used.
• - At high load, there are only minor losses in the power-optimized operation of the first control stage of the method according to the invention compared to the subsequent effect-optimized operation, since the efficiency curve according to the COP curves (cf. 3 ) is very flat at high temperatures and these losses are therefore almost negligible.

Reference List

1

Refrigerant circulation

2

refrigerant evaporator

3

refrigerant compressor

4

Refrigerant condenser, gas cooler

5

Expansion device, electric expansion valve

6

control unit

7

cycle-internal heat exchanger

8th

refrigerant collector

Claims (6)

Verfahren zum Betreiben einer Fahrzeug-Kälteanlage mit einem Kältemittelkreislauf (1), welcher als Komponenten wenigstens einen Kältemittelverdampfer (2), einen Kältemittelverdichter (3), einen Kältemittelkondensator, Gaskühler (4) und ein dem Kältemittelverdampfer (2) zugeordnetes und elektrisch mittels eines Steuergerätes (6) ansteuerbares Expansionsorgans (5) mit einer veränderbaren Ventil-Querschnittsfläche aufweist und bei einer angeforderten maximalen Kälteleistung zur Erreichung einer Ziellufttemperatur (T _soll ) nach dem Kältemittelverdampfer (2) folgende Verfahrensschritte aufeinanderfolgend durchgeführt werden: a) Regelung der Ventil-Querschnittsfläche des Expansionsorgans (5) zunächst auf einen optimalen Hochdruck (HD _opt ) und anschließend auf einen schrittweise in Richtung auf einen maximal zulässigen Hochdruck (HD _zul ) am Ausgang des Kältemittelkondensators, Gaskühlers (4) erhöhten Hochdruck, bis die Ziellufttemperatur (T _soll ) erreicht wird, oder der Hochdruck auf dem Niveau des maximal zulässigen Hochdruckes (HD _zul ) solange gehalten wird, bis die Ziellufttemperatur (T _soll ) erreicht wird, wobei die Bestimmung des optimalen Hochdrucks (HD _opt ) anhand eines Druck-COP-Diagramms in Abhängigkeit einer Umgebungs- oder Austrittstemperatur des Kältemittels am Austritt des Kältemittelkondensators, Gaskühlers (4), oder gemäß der Berechnungsvorschrift HD _opt = T _KM × 2 + 20 mit T _KM als Austrittstemperatur des Kältemittels am Kältemittelkondensator, Gaskühlers (4) erfolgt, b) Regelung der Ventil-Querschnittsfläche des Expansionsorgans (5) auf den zuletzt eingeregelten Hochdruckwert am Ausgang des Kältemittelkondensators, Gaskühlers (4) und Steuerung des Kältemittelverdichters (3) von einer bei dem zuletzt eingeregelten Hochdruckwert geförderten aktuellen Fördermenge auf eine reduzierte Fördermenge, solange die Ziellufttemperatur (T _soll ) eingehalten wird, und c) Regelung der Ventil-Querschnittsfläche des Expansionsorgans (5) in Richtung auf den optimalen Hochdruck (HD _opt ) am Ausgang des Kältemittelkon densator, gas cooler (4), either by increasing the valve cross-sectional area as long as the temperature after the refrigerant evaporator (2) corresponds to or falls below the target air temperature (T _set ) or by reducing the valve cross-sectional area as long as the temperature after the refrigerant evaporator (2) exceeds the target air temperature (T _set ). Method for operating a vehicle refrigeration system with a refrigerant circuit (1), which has as components at least one refrigerant evaporator (2), one refrigerant compressor (3), one refrigerant condenser, gas cooler (4) and an expansion element (5) associated with the refrigerant evaporator (2) and electrically controllable by means of a control unit (6) with a variable valve cross-sectional area and at a requested maximum refrigerating capacity to achieve a target air temperature (T_should) after the refrigerant evaporator (2), the following process steps are carried out in succession: a) Setting the valve cross-sectional area of the expansion device (5) to a defined starting cross-section and then to a step-by-step towards a maximum permissible high pressure (HP_allowed) at the outlet of the refrigerant condenser, gas cooler (4) increased high pressure until the target air temperature (T_should) is reached, or the high pressure is at the level of the maximum permissible high pressure (HP_allowed) is held until the target air temperature (T_should) is reached, b) Regulation of the valve cross-sectional area of the expansion element (5) to the last regulated high-pressure value at the outlet of the refrigerant condenser, gas cooler (4) and control of the refrigerant compressor (3) from a current delivery rate delivered at the last adjusted high-pressure value to a reduced delivery rate, as long as the target air temperature (T_should) is complied with, c) Control of the valve cross-sectional area of the expansion device (5) in the direction of an optimal high pressure (HP_opt) at the outlet of the refrigerant condenser, gas cooler (4), either by increasing the valve cross-sectional area, as long as the temperature after the refrigerant evaporator (2) meets the target air temperature (T_should) equals or falls below, or the valve cross-sectional area is reduced, as long as the temperature after the refrigerant evaporator (2) is the target air temperature (T_should) exceeds, whereby the determination of the optimum high pressure (HP_opt) based on a pressure-COP diagram depending on the ambient or outlet temperature of the refrigerant at the outlet of the refrigerant condenser, gas cooler (4), or according to the calculation rule HD_opt = T_KM × 2 + 20 with T_KM as the outlet temperature of the refrigerant at the refrigerant condenser, gas cooler (4). procedure after claim 1 or 2 , in which, following method step c, the vehicle refrigeration system is operated at an optimal high pressure at the outlet of the refrigerant condenser, gas cooler (4) while maintaining the target air temperature (T _set ) in a system operation effected by regulation of the refrigerant compressor (3). Method according to one of the preceding claims, in which the maximum permissible high pressure (HD _perm ) is monitored as the maximum permissible system operating pressure (HD _max ) at the outlet of the refrigerant compressor (3) and the non-exceeding of this maximum permissible system operating pressure (HD _max ) is ensured by controlling the valve cross-sectional area of the expansion element (5) or by controlling the refrigerant compressor (3). Vehicle refrigeration system for carrying out the method according to one of the preceding claims. Vehicle with a vehicle refrigeration system claim 5 .

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