DE10258524A1 - Refrigerant circuit for an automotive air conditioning system - Google Patents

Abstract

The invention relates to a refrigerant circuit for a motor vehicle air conditioning system, in which the refrigerant flows successively through a compressor, a refrigerant condenser, an expansion element regulating the refrigerant flow and an evaporator, each of which is connected to one another by a refrigerant line. It solves the task of designing the refrigerant circuit and the circuit management in such a way that its efficiency is increased in a simple manner. For this purpose, a liquid separator (6) with an outlet for liquid refrigerant is arranged between the expansion member (4) and the evaporator (7), which is connected upstream of the inlet of the evaporator (7), and the actuator of the expansion member (4) is via a thermomechanism Can be actuated, which is connected via a temperature sensor (5) to the refrigerant line at the outlet of the evaporator (7), which only carries evaporated refrigerant.

Description

The invention relates to a refrigerant circuit for a motor vehicle air conditioning system, in particular also for CO ₂ as a refrigerant (refrigerant R744).

In automotive air conditioning systems, the air the supplied to the passenger compartment is on a heat exchanger (Evaporator) cooled, where the refrigerant conducted in this evaporates and the for it required amount of heat deprived of air. In a cycle, the refrigerant through changes in state processed so that for cooling the Air a limited amount of refrigerant sufficient. In a second heat exchanger, the gas cooler or condenser (refrigerant condenser), becomes the refrigerant the supplied in the evaporator Amount of heat through outside air withdrawn again, for which purpose between the refrigerant and the outside air there must be a temperature difference. Therefore, the gaseous refrigerant compressed in a compressor and raised in temperature before passed it into the gas cooler and liquefied there becomes. There is also an expansion element between the evaporator and the gas cooler arranged to the compressed in the compressor and thus with a higher Pressure and with a higher Refrigerant with temperature again to relax and to regulate the refrigerant flow. The compressor and expansion valve separate the refrigerant circuit into one High pressure and a low pressure area. Usually located in High pressure area, i.e. in the area of the compressed refrigerant also a refrigerant collector between the compressor and the expansion device, in which the highly hygroscopic refrigerant is dried, about corrosion damage to avoid in the compressor.

Because of the quick change the operating conditions due to the vehicle movement with changing Travel speeds and different heat input, the cooling requirement is subject to large fluctuations, to which the cooling capacity of the Compressor must adjust. A capacity control in the refrigerant circuit is mainly done by regulation of the mass flow rate of the evaporator passing through it Refrigerant. This is done, for example, by controlling the compressor delivery volume, throttling or deriving, however, these methods the refrigerant circuit complicate and additional Components require. A known fluid control device is a thermostatic expansion valve that prevents overheating of the evaporated refrigerant can be controlled at the outlet of the evaporator. To operate of the expansion valve under changing operating conditions part of the evaporator for overheating of the refrigerant used.

In the DE 689 08 181 T1 (WO 90/07683) describes a method for operating a refrigerant circuit in an air conditioning system, in which supercritical pressure is used on the high pressure side. This method provides that the pressure on the high pressure side, that is to say before the expansion, is regulated by changing the respective refrigerant charge on the high pressure side. A refrigerant buffer tank arranged in the refrigerant circuit is used for this. By reducing the content of the same, the pressure is increased and vice versa, which in turn affects the specific capacity of the refrigerant circuit.

Furthermore, WO 00/03883 describes a CO ₂ -operable air conditioning system for a motor vehicle, in which a fixed throttle is provided in the refrigerant circuit as an expansion element, the throttle opening of which is matched in length and diameter to the system in such a way that in all Operating conditions the pressure in the high pressure section is limited to values of less than 14 Mpa. This ensures that the air conditioning system is operated in every operating state at the high pressure in which the optimum of the cooling capacity and the optimum of the coefficient of performance lie. This air conditioning system can be produced at a reduced cost by using a fixed throttle, which promotes the use of the environmentally friendly CO ₂ refrigerant in a vehicle air conditioning system, which is normally associated with an increase in the cost of such a system compared to the use of other refrigerants.

It is the task of the ending, one Refrigerant circulation according to the preamble of claim 1 and the refrigeration cycle to shape that Efficiency is increased in a simple manner.

This task is done in a refrigerant cycle according to the preamble of claim 1 by its characterizing Features and a method with the features of claim 5 solved.

The proposed refrigerant circuit consists of a compressor, at the output of which a high-pressure section with a gas cooler and on the suction side (compressor inlet) of a low-pressure section with an evaporator are connected, and an adjustable expansion element connecting the high-pressure section to the low-pressure section, with the low-pressure section downstream of the expansion device a liquid separator is arranged with an outlet for separated liquid refrigerant, which is connected to the inlet of the evaporator. The actuator of the expansion element is integrated to regulate the refrigerant flow Thermomechanism can be actuated, which is connected to the refrigerant line at the evaporator outlet via a temperature sensor. Instead of the thermal sensor, refrigerant vapor escaping from the evaporator can also be passed through the thermomechanism. The liquid separator ensures that only liquid refrigerant enters the evaporator. The refrigeration cycle is set so that the refrigerant evaporates completely in the evaporator.

This is confirmed by a corresponding Recycling and overheating of the refrigerant vapor generated in the evaporator reached, the temperature of the refrigerant at the evaporator outlet is important. If this is too high, the overheating will occur too large, becomes the refrigerant mass flow increased by the expansion organ. If the temperature is too low, and thus the overheating is too low, the refrigerant mass flow reduced. An increase the degree of efficiency with constant compressor performance and constant Fuel consumption caused by the compressor is thus in a simple way on the low pressure side due to an increased refrigerant mass flow reached by the expansion valve and the liquid separator. The fuel consumption is not increased. In this refrigerant cycle no accumulator is needed, fluctuating refrigerant requirements in the refrigerant circuit compensate. This takes over the Liquid separator. Because at the evaporator outlet only overheated Refrigerant vapor gets into the suction line of the compressor, there is no need for an accumulator, the still fluid refrigerant withhold to protect the compressor from liquid hammer. This Refrigerant circulation is fundamental with the usual refrigerants operated.

The liquid separator can also be used an exit for the gaseous Provide refrigerant be the one over a throttle body with the evaporator outlet-side refrigerant line, which is also the suction line of the compressor, is connected. About this Output is at high cooling capacity, leading to greater overheating and an elevated Refrigerant mass flow rate leads, one by resulting excess gas in the liquid separator dissipated the required refrigerant mass flow on liquid refrigerant to the evaporator.

An internal heat exchanger can also be arranged on the high-pressure side in the outlet line of the refrigerant condenser, through which the high-pressure cooled refrigerant is passed to the expansion element and the overheated, relaxed refrigerant to the compressor, so that the refrigerant to be expanded and evaporated is cooled, with the result that the amount of liquid in the refrigerant increases after expansion, so more liquid refrigerant is available for evaporation. The internal heat exchanger thus increases the cooling capacity and also the efficiency of the cooling circuit. An internal heat exchanger is also advantageous because of the rapid change in operating conditions. This version with an internal heat exchanger is particularly suitable for CO ₂ refrigerants.

A is advantageously used as an expansion element thematic expansion valve used. When starting the Air conditioning is overheating Evaporator outlet increased, so that Expansion valve opens wide and the refrigerant mass flow is increased, whereby in the shortest possible time Time the maximum cooling capacity is achieved.

The invention is illustrated below of embodiments explained. In the accompanying drawings show schematically:

1 : a refrigerant circuit for CO ₂ refrigerants with an internal heat exchanger and

2 : A refrigerant circuit for CO ₂ refrigerants with an internal heat exchanger, with a gas bypass and a throttle element arranged in this.

The in 1 The refrigerant circuit shown has a compressor one after the other in the circuit direction 1 , a gas cooler (refrigerant condenser) 2 , an internal heat exchanger 3 with a first refrigerant line coil 3.1 , a thermostatic expansion valve 4 known type with a thermostatic sensor 5 , a liquid separator 6 with an outlet in its lower part for liquid refrigerant separated in it, an evaporator 7 , at the output of which the sensor 5 is arranged, and the heat exchanger 3 with a second refrigerant line coil 3.2 in front of the compressor 1 on.

The CO ₂ refrigerant on the suction side of the compressor 1 has a pressure of about 35 to 45 bar and a temperature of about 20 ° C in the compressor 1 compressed to a pressure of essentially 110 bar, the temperature of the refrigerant rising to approximately 100 ° C. In the gas cooler 2 the refrigerant is cooled to approx. 55 ° to 60 ° C by flowing outside air and liquefied in the process. The heat extracted from the CO ₂ refrigerant is dissipated with the outside air. In the inner heat exchanger 3 gives that through the line queue 3.1 flowing CO ₂ refrigerant heat to the through the conduit 3.2 flowing refrigerant, which is integrated into the suction line of the compressor, wherein it is cooled to a temperature of substantially 25 ° C. In the expansion valve 4 is the liquid CO ₂ refrigerant, which has a pressure of about 110 bar and a temperature of substantially 25 ° C on the high pressure side, in the wet vapor state, whereby it is at a pressure of 35 to 45 bar relaxed and a temperature of 0 ° to 10 ° C is cooled. In this state, the CO ₂ refrigerant gets into the liquid separator 6 , in the lower part of which the liquid phase settles. Via the outlet on the liquid separator 6 only liquid CO ₂ refrigerant gets into the evaporator 7 , by absorbing heat from the outside or recirculated air to be cooled for the passenger compartment at a constant pressure of 35 to 45 bar, which corresponds to the suction pressure at the compressor 1 corresponds, evaporates. The expansion valve 4 as an adjustable mass flow valve is set so that the expansion valve for cooling the air 4 passing refrigerant mass flow is set so that the refrigerant in the evaporator 7 is completely converted into the gaseous state and is overheated by about 2 ° to 4 ° C. at the evaporator outlet. With an increased cooling capacity required, that is, when the CO ₂ refrigerant has to absorb more heat from the outside or recirculating air, the proportion of the gaseous phase in the evaporator increases 7 and with it the overheating and it gets over the sensor 5 the valve opening in the expansion valve 4 expanded so that the refrigerant mass flow is increased and the overheating is reduced.

At the in 2 The refrigerant circuit shown, which apart from the liquid separator has the same components as the one described above and has this in the same order and which is also preferably operated with CO ₂ refrigerant, is a liquid separator instead of the liquid separator described there 8th arranged. This also has an outlet for gaseous refrigerant via a gas bypass 9 in which a fixed throttle 10 is arranged with the suction line 11 of the compressor 1 connected is.

With higher cooling capacity, this leads to an increased CO ₂ refrigerant mass flow rate at the expansion valve 4 leads, is also the gas portion of the through the expansion valve 4 relaxed and thereby converted into a wet vapor state of CO ₂ refrigerant. So that the liquid volume in the liquid separator 8th remains constant and does not shrink due to the increased mass flow, excess gas is passed through the gas bypass 9 and the fixed throttle arranged in this 10 derived and the superheated steam in the outlet line of the evaporator 7 that of the suction line 11 of the compressor 1 corresponds in the area between the sensor 5 and the internal heat exchanger 3 fed. A ratio of 1: 4 of gaseous to liquid CO ₂ refrigerant is preferably set. A gas portion exceeding 20% as a result of an increased mass throughput is thus via the fixed throttle 10 dissipated. The regulation of the expansion valve 4 through on the evaporator 7 escaping superheated CO ₂ refrigerant vapor is in the arrangement described by the gas bypass 9 not affected. The measure ensures that even with a high required cooling capacity at the inlet of the evaporator 7 only liquid CO ₂ refrigerant is available.

1

compressor

2

gas cooler

3

heat exchangers

3.1

Refrigerant piping snake

3.2

Refrigerant piping snake

4

expansion valve

5

sensor

6

liquid separator

7

Evaporator

8th

liquid separator

9

Gas bypass

10

fixed throttle

11

suction

Claims (9)

Refrigerant circuit for a motor vehicle air conditioning system, in which the refrigerant flows in succession through a compressor, a refrigerant cooler as a refrigerant condenser, an expansion element regulating the refrigerant flow and an evaporator, which are each connected to one another by a refrigerant line, characterized in that between the expansion element ( 4 ) and the evaporator ( 7 ) a liquid separator ( 6 ) is arranged with an outlet for liquid refrigerant, which is connected to the inlet of the evaporator ( 7 ) and that the actuator of the expansion element ( 4 ) can be operated via a thermomechanism which is activated via a temperature sensor ( 5 ) with the refrigerant line at the evaporator outlet ( 7 ) that only carries evaporated refrigerant. Refrigerant circuit according to claim 1, characterized in that the liquid separator ( 6 ) has an outlet for gaseous refrigerant, which is connected to the suction line ( 11 ) of the compressor ( 1 ) via a throttle device ( 10 ) connected is. Refrigerant circuit according to claim 1 or 2, characterized in that in the outlet line of the refrigerant condenser ( 2 ) an internal heat exchanger ( 3 ) with the suction line ( 11 ) of the compressor ( 1 ) is formed. Refrigerant circuit according to claim 1, characterized in that the expansion element is a thermostatic expansion valve ( 4 ) is. Method for operating a motor vehicle air conditioning system with a refrigerant circuit, in which gaseous refrigerant is compressed and heated in a compressor, conveyed by a heat exchanger, cooled and liquefied therein, then in expanded in an expansion device and returned to the gaseous state in an evaporator used as a heat exchanger and sucked in by the compressor, characterized in that the expansion device ( 4 ) relaxed refrigerant via a liquid separator ( 6 ) from which only liquid refrigerant to the evaporator ( 7 ) flows, and that the refrigerant mass flow, which is the low pressure side of the expansion element ( 4 ) and the liquid separator ( 6 ) flows through one at the outlet of the evaporator ( 7 ) set overheating is regulated. A method according to claim 5, characterized in that a in the liquid separator ( 6 ) resulting excess gas in the suction line ( 11 ) of the compressor ( 1 ) is conducted. Method according to Claim 5 or 6, characterized in that between the compressor ( 1 ) sucked in gaseous refrigerant and by the in the refrigerant condenser ( 2 ) cooled refrigerant heat exchange takes place. A method according to claim 5 or 6, characterized in that that this refrigerant R134a is. A method according to claim 7, characterized in that the refrigerant is R744 (CO ₂ refrigerant).