EP1559970A2 - Method and device for pressure control in a refrigeration cycle - Google Patents

Abstract

The compressor (14), condenser (6) and evaporator (8) form a refrigeration circuit with an expansion valve (12). The condenser pressure is monitored by a sensor (19) and the evaporator temperature by a sensor (16) which feed a high pressure controller (24) and limiter (28) and a temperature control unit (18,20). The values are compared to reference values (SW(VT)) and (SW(HD)) to regulate the compressor through a control unit (22) and a pulse width modulator (32).

Description

The invention relates to a method and a device for pressure control in a refrigerant circuit of an air conditioner for a vehicle.

To improve interior comfort and thermal comfort in a vehicle is generally an air conditioning system (also called air conditioning) used, at least from a heating and Refrigerant circuit, an air conditioner and an air guide is formed. in the Heating and refrigerant circuit, z. B. a so-called R744 refrigerant circuit (CO2), can under unacceptable conditions unacceptably high Pressure peaks occur. For example, it comes to high pressure peaks in the so-called "hot start" associated with very high standstill pressures or in the case of a sudden increase in the engine and thus the Compressor speed.

To avoid such inadmissible high pressure peaks it is on the one hand known to provide a pressure relief valve in the refrigerant circuit. The pressure relief valve is used as an additional component in or integrated on the compressor. This in turn leads to an increased space requirement, at extra cost and increased weight. On the other hand it is known to provide a rupture disk in the refrigerant circuit. The normally always existing rupture disc may only in absolute exceptional case address, since this process is irreversible. An exceptional case is only when one or more faults in the air conditioning system occur given. Under normal operating conditions, which are also extreme can, the response of the rupture disc is not acceptable.

The object of the invention is therefore a method and a device to specify for pressure control in a refrigerant circuit, which without additional components provide comprehensive protection against impermissibly high Offers pressure peaks.

According to the invention the object is achieved by a method with the features of claim 1 and by a device with the features of Claim 9. Advantageous developments are the subject of the dependent claims.

In the method for pressure control in a refrigerant circuit of an air conditioner for a vehicle is in a basic control loop (also superordinate Called a setpoint for an evaporator temperature, the one evaporator temperature controller for forming a manipulated variable is supplied. Based on the manipulated variable of the evaporator temperature controller a high-pressure setpoint is determined for a high-pressure regulator, whereby the Prevention of pressure peaks by means of the high-pressure regulator on the basis of High pressure setpoint a primary and in addition by means of a high pressure limitation a secondary control variable to a regulation of the high pressure be determined.

In other words, in the method for pressure regulation in a refrigerant circuit, in which in a base control loop, a setpoint for an evaporator temperature is given, the one evaporator temperature controller leads, with a setpoint for the high pressure by means of a basic characteristic derived from the manipulated variable of the evaporator temperature controller and possibly by a correction characteristic is modified and the thus obtained setpoint for the high pressure is supplied to a high-pressure regulator, the first manipulated variable (= primary manipulated variable) is determined, in addition a second manipulated variable (= secondary control variable) in an additional control circuit for high pressure limitation (called high-pressure limitation for short).

Depending on the type and design of the method for pressure control, the primary or the secondary manipulated variable with a transfer characteristic in Pulse width modulated control signal implemented, which is a control valve for Controlling the stroke volume of a compressor, in particular a refrigerant compressor, is supplied.

In a possible embodiment of the high-pressure limitation as a PD or PID controller, the high pressure set point is increased by one pressure value. Subsequently the difference between the high pressure limitation as an input variable of the pressure value modified high pressure setpoint and the high pressure actual value fed. Ie. which is designed as an additional regulator High pressure limitation is a by a predetermined pressure value, eg. B. 10 bar to 15 bar, raised high pressure setpoint supplied. The Control value of the high-pressure controller (= primary control value) and the manipulated variable the other controller (= secondary manipulated variable) are then closed linked to a common manipulated variable. In particular, the common manipulated variable through a MIN function (= minimum value generation) educated. The common manipulated variable, which is the result of this linkage is (also called resulting manipulated variable), is determined by a transfer characteristic in the pulse width modulated control signal for controlling the Compressor stroke volume implemented.

In an alternative embodiment of the high-pressure limitation as a comparator this is fed to the high pressure actual value. The comparator can both in terms of software and in time-critical cases in terms of hardware, z. B. in analog circuit technology, be formed. By comparing a given Maximum value for the high pressure setpoint with the high pressure actual value, for example by means of a two-point controller with switching hysteresis, the secondary manipulated variable is determined. In parallel, by means of the High-pressure controller the primary control value with a transfer characteristic in implemented a pulse width modulated primary manipulated variable. The pulse width modulated primary control variable and the determined by the comparator Result of the comparison (= secondary manipulated variable) are given by an AND function linked to a common manipulated variable (= resulting manipulated variable), in this embodiment, the control signal for the control valve forms the control of the stroke volume of the compressor.

In contrast to the dynamic or PD controller designed as a PD or PID controller High-pressure limitation, the limiting function of the comparator acts statically and not continuously, but as a pure ON / OFF function. A The resulting system unrest can occur in some air conditioning systems be acceptable.

In another alternative embodiment, there is no complete shutdown, but a continuous reduction over one Limiting characteristic. As a result, the process may under certain circumstances be improved during a launch phase.

In all proposed methods for high-pressure limitation can also included an existing magnetic coupling of a refrigerant compressor for example, as a superimposed ON / OFF function acts.

In a preferred embodiment for a device for pressure control in a refrigerant circuit of an air conditioner, this comprises a basic control loop to determine a set point for the evaporator temperature and a downstream evaporator temperature controller, via whose Control value is a high pressure setpoint is determined, the Evaporator temperature controller a high-pressure regulator to determine the primary command value for the high pressure and a high pressure limit to Determination of the secondary control value for the high pressure downstream are. The high-pressure limitation is preferably parallel to the high-pressure regulator connected.

The advantages achieved by the invention are in particular that without additional components, such as pressure relief valve or rupture disk, comprehensive protection against impermissibly high pressure peaks in the refrigerant circuit an air conditioner for a vehicle may be pure is procedurally possible, in addition to the primary control value of High-pressure regulator by means of a high-pressure limitation a secondary Manipulated variable for forming a control signal for a compressor control valve for the purpose of controlling the stroke volume. Such a solution brings advantages through reduced installation space and weight of the Refrigerant cycle, a high level of operational safety through an automatic Protective function and avoidance of response irreversible Protective devices (such as a rupture disk) and the associated Expenses for the recovery.

Fig. 1

schematisch eine Vorrichtung zur Druckregelung in einem Kältemittelkreislauf mit einer als PD-Regler ausgebildeten Hochdruck-Begrenzung,

Fig. 2

schematisch eine alternative Ausführungsform für eine Vorrichtung zur Druckregelung in einem Kältemittelkreislauf mit einer als Komparator ausgebildeten Hochdruck-Begrenzung,

Fig. 3

schematisch eine alternative Ausführungsform für eine Vorrichtung zur Druckregelung in einem Kältemittelkreislauf mit einer kontinuierlichen Hochdruck-Begrenzung, und

Fig. 4

ein Diagramm für eine Begrenzungskennlinie in Abhängigkeit vom Hochdruck-Istwert zur Bestimmung eines Stellsignals für ein Kältemittel-Kompressorventil.

Embodiments of the invention will be explained in more detail with reference to a drawing. Show:

Fig. 1

schematically a device for pressure control in a refrigerant circuit with a designed as a PD controller high pressure limitation,

Fig. 2

2 schematically shows an alternative embodiment of a device for pressure regulation in a refrigerant circuit with a high-pressure limitation designed as a comparator,

Fig. 3

schematically an alternative embodiment of a device for pressure control in a refrigerant circuit with a continuous high-pressure limitation, and

Fig. 4

a diagram for a limiting characteristic as a function of the high pressure actual value for determining a control signal for a refrigerant compressor valve.

Corresponding parts are in all figures with the same reference numerals Mistake.

In Fig. 1 is a device 1 for pressure control in a refrigerant circuit 2 of an air conditioning system 4 (also called air conditioning) for a Vehicle shown. The air conditioning system 4 can also be used as a combined Device for cooling or heating in a closed Space, z. B. in the vehicle interior, to be formed leading air. The air conditioning system 4 comprises a gas cooler 6, an evaporator 8 and an interposed inner heat exchanger 10, in which a cycle process underlying air conditioning or cooling to run the air conditioning system 4 and vice versa can, so that the air conditioning system 4 also acts as a heat pump. The heat pump operation is not the subject of the application. following the air conditioning system 4 for the refrigerant circuit 2 is closer described.

The refrigerant circuit 2 represents a closed system in which a refrigerant KM, z. As carbon dioxide, R134a, R177, from the gas cooler 6 via the inner heat exchanger 10 is led to the evaporator 8 in the circuit. The refrigerant KM takes heat from one into the vehicle flowing air and releases it to the ambient air again. For this It is necessary that the refrigerant KM has a sufficiently large temperature difference has to the air. For this purpose, the cooling of the refrigerant takes place KM arranged by pressure loss at one in the refrigerant circuit 2 Expansion organ 12; the cooling of the inside of the vehicle flowing air takes place by heat absorption of the refrigerant KM in the evaporator 8th.

In detail, the refrigerant circuit 2 includes, for example, the engine the vehicle driven compressor 14 or compressor with a variable Stroke volume H for compression of a gaseous refrigerant KM, z. B. carbon dioxide. The compressor 14 sucks the gaseous refrigerant KM from the evaporator 8 via the expansion device 12 coming on. The sucked gaseous refrigerant KM has a low temperature and a low pressure. The refrigerant KM is under the compressor 14 under Heating compresses and changes its state of aggregation from gaseous after liquid with simultaneous heating. The gaseous and hot Refrigerant KM is the heat exchanger 6, z. B. a gas cooler or Capacitor, guided. Due to the air flowing into the gas cooler 6 air the refrigerant KM is cooled.

The cooled in the gas cooler 6 refrigerant KM becomes the subsequent suction pressure side supply of the compressor 14 via the inner heat exchanger 10 and passed over the expansion member 12, which as throttle is working. It comes here to a relaxation of the refrigerant KM, so that the coolant KM cools down considerably. By means of the expansion organ 12 the cooled refrigerant KM is injected into the evaporator 8, where the Refrigerant KM of the incoming air, z. B. fresh air, the required heat of evaporation withdraws. This cools the air. The cooled air is via a fan not shown in detail and air ducts in led the vehicle interior. The refrigerant KM is after the evaporator 8 on the inner heat exchanger 10 suction pressure side of the compressor 14 fed again.

To avoid high pressure peaks in the refrigerant circuit 2, z. For example Hot start or sudden increase in speed of the compressor 14, comprising the device 1 for pressure control of the refrigerant circuit 2 an extended Evaporator temperature control, which is described in more detail below becomes. The evaporator temperature control includes a modified subordinate one Refrigerant high pressure control, in addition to the well-known refrigerant high pressure control According to the prior art, a highly dynamic Protection mechanism to avoid pressure peaks in the form of a Has additional control loop.

By a higher-level control, not shown here, a setpoint SW (VT) for an evaporator temperature VT specified, z. B. sliding from 2 ° C to 12 ° C. By means of a temperature sensor 16, the actual value IW (VT) for the evaporator temperature VT at the evaporator 8 determined. The difference from the setpoint SW (VT) and the actual value IW (VT) for the evaporator temperature VT is a evaporator temperature controller 18, for example a PI controller supplied. From the manipulated variable U of Evaporator temperature controller 18 is by means of a base characteristic 20 a Setpoint SW (HD) for the high pressure HP of the refrigerant KM in Refrigerant circuit 2 derived after the gas cooler 6.

Due to the material properties of the refrigerant KM, z. From R744 may require an additional correction characteristic 22, with the setpoint value SW (HD) obtained from the basic characteristic curve for the High pressure HD is modified to be a corrected or modified one High pressure setpoint SW (HDm) to obtain. As inputs E1 to En for the correction of the set value SW (HD) for the high pressure HD on the basis of Correction characteristic curve 22 serve, for example, the air inlet temperature, the Air inlet moisture, the amount of air and / or the speed of the compressor 14th

Furthermore, to determine the high pressure actual value IW (HD) a pressure sensor 19 provided, the high pressure HD in the refrigerant circuit 2 after the gas cooler 6 determined. The difference from the modified high pressure setpoint SW (HDm) and the high pressure actual value IW (HD) becomes one High pressure regulator 24 supplied as a pressure difference value Δp. Based on the Pressure difference value .DELTA.p is a primary by means of the high-pressure regulator 24 Control value Up for the high pressure HD for controlling the stroke volume H of the Compressor 14 determined by means of a control valve 26.

The high-pressure regulator 24 is a high pressure limitation as an additional control loop 28 assigned. By means of the high-pressure limitation 28 is for adjustment the high pressure HD after the gas cooler 6 in addition to the primary control variable Up a secondary control variable Us for the control valve 26 of the compressor 14 determined. The high-pressure limitation 28 (also additional high-pressure refrigerant control called) acts as a protective mechanism for Avoiding unwanted high pressure peaks. This is the high pressure limit 28 parallel to the regular high pressure control - to the high pressure regulator 24 - switched.

The high-pressure limitation 28 becomes a pressure difference value Δp from modified High pressure setpoint SW (HDm) and high pressure actual value IW (HD) fed. Preferably, the modified high pressure set point SW (HDm) by a pressure value p, for example 10 bar to 15 bar, raised so that possibly no premature high-pressure limiting measure is triggered. The high-pressure limitation 28 is, for example, as a PD or PID controller R formed. Advantageously, in a PID controller at any high-pressure peaks high dynamic the stroke volume H of the Compressor 14 can be reduced.

The secondary manipulated variable Us of the high-pressure limitation 28 is connected to the primary Manipulated variable Up of the high-pressure regulator 24 via a MIN element 30 (= MIN function) linked. The result of the link is a Resulting manipulated variable Ug, which avoids highly dynamic pressure peaks. The common manipulated variable Ug is by means of a pulse width modulator 32nd based on a transfer characteristic in a pulse width modulated control signal S implemented. Subsequently, the pulse width modulated actuating signal S is the Control valve 26 of the compressor 14 for controlling the stroke volume H. fed.

In Fig. 2 is another alternative, in particular simple embodiment for the device 1 for pressure control with a static secondary Pressure peak limitation by an extended evaporator temperature control shown.

It is used as a high-pressure limiting 28 for determining the secondary control variable Us a comparator K provided. This is the high pressure limit 28, the high pressure actual value IW (HD) supplied. The comparator K points a hysteresis two-point behavior with a fixed predetermined Maximum value for the high pressure setpoint SW (HD) to. On the other hand the steady Function of dynamic as PD or PID controller R working High pressure limitation 28 of FIG. 1 are in the as comparator K. As a result, only working high-pressure static limitation 28 in Fig. 2 two switching states for the secondary manipulated variable Us set.

To control the control valve 26, the primary control variable Up means a pulse width modulator 32 based on a transfer characteristic in a Pulse-width modulated primary manipulated variable RPM implemented via an AND gate 34 (= AND function) with the secondary manipulated variable Us to a control signal S for controlling the control valve 26 is linked. Thus, the effect Limiting function in this embodiment shown in FIG. 2 not continuous, but as a pure ON / OFF circuit that only is activated for unauthorized high pressure values. This results in an increased System unrest, which can be accepted under certain circumstances. The comparator K can be used both as a software module and in time-critical Cases hardware, z. B. in analog circuit technology be.

FIG. 3 shows a further alternative embodiment for the device 1 for pressure control with a dynamic pressure peak limitation by an expanded evaporator temperature control shown. The high pressure limitation 28 takes place to determine the secondary manipulated variable Us continuously over the exemplary characteristic of FIG. 4.

The secondary control variable Us the high-pressure limitation 28 is connected to the primary manipulated variable Up of the high-pressure regulator 24 via a MIN element 30 (= MIN function) linked. The resulting manipulated variable Ug is determined by means of a Pulse width modulator 32 based on a transfer characteristic in a pulse width modulated control signal S implemented. Subsequently, the Control signal S the control valve 26 of the compressor 14 for controlling the Stroke volume H supplied.

LIST OF REFERENCE NUMBERS

1

Device for pressure control

2

Refrigerant circulation

4

Cooling system

6

gas cooler

8th

Evaporator

10

internal heat exchanger

12

expansion element

14

compressor

16

temperature sensor

18

Evaporator temperature controller

19

pressure sensor

20

Base curve

22

Correction characteristic

24

High-pressure regulator

26

control valve

28

High pressure limiting

30

MIN link

32

Pulse width modulator

34

AND gate

E1 to En

input variables

H

Stroke volume of the compressor

HD

high pressure

IW (HD)

High-pressure actual value

IW (VT)

Evaporator temperature value

K

comparator

KM

refrigerant

p

pressure value

Ap

Differential pressure value

R

PD or PID controller

S

Control signal for control valve

SW (HD)

High pressure setpoint

SW (HDM)

modified high pressure setpoint

SW (VT)

Evaporator temperature setpoint

U

Control value for evaporator temperature

Ug

common control variable for high pressure

up

primary control value for high pressure

rpm

pulse width modulated primary control value for high pressure

Us

secondary control variable for high pressure

Claims (20)

Method for pressure regulation in a refrigerant circuit (2) of a Air conditioning (4) for a vehicle in which a basic control loop a desired value (SW (VT)) for an evaporator temperature (VT) which is an evaporator temperature controller (18) to the formation a manipulated variable (U) is supplied, based on the manipulated variable (U) a high pressure set point (SW (HD), SW (HDm)) for a high pressure regulator (24) is determined and by means of the high-pressure regulator (24) based on the high pressure setpoint (SW (HD), SW (HDm)) a primary Control value (Up) and by means of a high-pressure limitation (28) a secondary manipulated variable (Us) to a regulation of high pressure (HD) be determined. Method according to Claim 1, in which the high-pressure boundary (28) is switched parallel to the high-pressure regulator (24). The method of claim 1 or 2, wherein in a PD or PID controller (R) designed high pressure limiting (28) the high pressure setpoint (SW (HD), SW (HDm)) is increased by one pressure value (p) becomes. Method according to one of claims 1 to 3, wherein in a than Comparator (K) formed high pressure limitation (28) of this High pressure actual value (IW (HD)) is supplied. Method according to one of claims 1 to 4, wherein the primary Control value (Up) and the secondary control value (Us) for the high pressure (HD) circuitry to a common manipulated variable (Ug) to Control of high pressure (HD) are linked. Method according to Claim 5, in which the primary manipulated variable (Up) and the secondary control variable (Us) for regulating the high pressure (HD) linked via a MIN function. Method according to Claim 5, in which the primary manipulated variable (Up) and the secondary control variable (Us) for regulating the high pressure (HD) be linked by means of an AND function. Method according to one of claims 1 to 7, wherein one of the manipulated variables (Up, Us, Ug) to control high pressure (HD) a transfer characteristic in a control signal (S) for controlling the Stroke volume (H) of a compressor (14) is implemented. Device (1) for pressure regulation in a refrigerant circuit (2) of a Air conditioning system for a vehicle having a base control circuit for detection a desired value (SW (VT)) for an evaporator temperature (VT) and a downstream evaporator temperature controller (18), Based on its manipulated variable (U) a high pressure setpoint (SW (HD)), SW (HDm)) is determined, wherein the evaporator temperature controller (18) a high-pressure regulator (24) for determining a primary Control value (Up) and a high pressure limit (28) for determination a secondary control variable (Us) for regulating the high pressure (HD) are downstream. Apparatus according to claim 9, wherein the high pressure restriction (28) connected in parallel to the high pressure regulator (24). Apparatus according to claim 9 or 10, wherein the high pressure Begrenzüng (28) is designed as a PD or PID controller (R). Apparatus according to claim 11, wherein the as PD or PID controller (R) trained high-pressure restriction (28) a subtractor for Determination of a pressure difference value (Δp) from high pressure setpoint (SW (HD), SW (HDm)) and high pressure actual value (IW (HD)) is. Apparatus according to claim 9 or 10, wherein the high pressure limitation (28) is designed as a comparator (K). Apparatus according to claim 13, wherein the comparator (K) is analogous Circuitry or designed as a software module. Apparatus according to claim 13 or 14, wherein the comparator (K) trained high pressure limitation (28) as an input High pressure actual value (IW (HD)) can be supplied. Apparatus according to claim 9 or 10, wherein the high pressure limitation (28) via a characteristic as a function of the high pressure actual value (IW (HD)). Device according to one of claims 9 to 16, wherein the primary Manipulated variable (Up) and the secondary manipulated variable (Us) for controlling the High pressure (HD) via an AND gate (34) can be linked. Device according to one of claims 9 to 16, wherein the primary Manipulated variable (Up) and the secondary manipulated variable (Us) for controlling the High pressure (HD) via a MIN element (30) are connectable. Device according to one of claims 9 to 18, wherein a pulse width modulator (32) for forming a pulse width modulated actuating signal (S) for a control valve (26) of a refrigerant compressor (14) is provided. Device according to one of claims 9 to 19, wherein as a high pressure limitation (28) a magnetic coupling of the refrigerant compressor (14) is provided as a superposed ON / OFF function.

Images