DE102007045765A1 - Refrigerant circulating apparatus, e.g. for air conditioning system, has expansion valve opening controlled to adjust refrigerant pressure and prevent overheating after start-up - Google Patents

Abstract

In refrigerant (RF) circulation apparatus, in which RF is compressed (1), cooled (2), decompressed through an expansion valve (4), evaporated (5) and recompressed, valve opening is controlled (10) so that the high pressure side RF pressure is at a first or second theoretical value (P1, P2), P1 being the optimum value. After starting the compressor, the pressure is set to P2 (lower than P1) for a specific time (t1), after which pressure is adjusted to P1. In refrigerant (RF) circulation apparatus, in which RF is compressed (1) above a critical pressure, cooled (2), decompressed through an expansion valve (4), evaporated (5) and returned to the compressor, the degree of opening of the valve is controlled (10) such that the RF pressure on the high pressure (pre-decompression) side is at a first or second theoretical value (P1, P2). P1 is the optimum value based on the temperature of RF flowing from the cooler. After starting the compressor, the pressure is set at P2 (lower than P1) for a predetermined time (t1), after which the pressure is adjusted to P1. An independent claim is included for a corresponding controlling method, involving: (A) determining whether the elapsed time (t) after starting the compressor (1) is less than t1; (B) setting P1 based on the temperature of RF flowing out of the cooler (2) so that the efficiency of the RF cycle is maximized; (C) setting P2; and (D) controlling the degree of opening of the expansion valve (4) so that the RF pressure before decompression is (i) at P2 when t is less than t1 and (ii) at P1 when t is not less than t1.

Description

The The present invention relates to a refrigerant cycle device and a control method for it.

Conventionally, a refrigerant cycle device uses carbon dioxide (CO ₂ ) as a refrigerant. In this case, a pressure of the refrigerant on a high pressure side before its decompression may be higher than a critical pressure of the refrigerant. A refrigerant pressure at a radiator outlet, in which an efficiency (COP) of a refrigerant circuit is maximized, changes according to a refrigerant temperature at the radiator outlet.

For example, the JP 9-264622 A a method for controlling a refrigerant cycle device. In the method, a refrigerant temperature at a radiator outlet is detected, and a target refrigerant pressure at the radiator outlet is set based on the detected refrigerant temperature so that the COP of the refrigerant circuit is maximized. Then, an opening degree of an expansion valve is controlled so that an actual refrigerant pressure reaches the target pressure, whereby the refrigerant cycle device is controlled with a high efficiency.

The JP 2000-88364 A discloses another method for controlling a refrigerant cycle device. In the method, a cooling capacity of the refrigerant cycle device is controlled by changing a rotational speed of a compressor. In addition, when the rotational speed of the compressor is high (ie, high load state), the target pressure is set to a first target pressure. In contrast, when the speed of the compressor is low (ie, low load state), the target pressure is set to a second target pressure that is lower than the first target pressure.

If the refrigerant cycle device is stopped in a case when a heat load condition becomes a high load condition is, i. an outside air temperature is high, a refrigerant pressure rises according to the outside air temperature. additionally becomes a difference between the outside air temperature and a refrigerant temperature on the radiator reduces, thereby reducing the cooling capacity the refrigerant cycle device is reduced. Therefore, when the refrigerant cycle device increases its Operation starts when the outside air temperature is high, a refrigerant pressure at a compressor outlet immediately after the start of operation of Refrigerant circuit device and the start of the compressor quickly and the refrigerant temperature can over a limit temperature of the compressor are. The limit temperature is a durability of a non-metal element in the compressor, e.g. a rubber element for sealing. Therefore, if the refrigerant temperature above the Limit temperature is reduced, a durability of the compressor is reduced be.

JP 9-264622 A and JP 2000-88364 A do not deal with a problem of the rapid rise of the refrigerant temperature when the outside air temperature is high, and do not reveal a solution to the problem.

In In view of the aforementioned problems, an object of the present invention Invention, a refrigerant cycle device to create a rise in a refrigerant temperature at one Compressor outlet over a limit temperature of the compressor immediately after the start of operation the refrigerant cycle device can prevent. Another object of the invention is to A method of controlling a refrigerant cycle device to provide an increase in a refrigerant temperature at a Compressor outlet over a limit temperature of the compressor immediately after the start of operation the refrigerant cycle device can prevent.

According to one Aspect of the invention includes a Refrigerant circuit device a compressor, a cooler, an expansion valve, an evaporator and a controller. The compressor compresses the refrigerant higher than a critical pressure of the refrigerant. The cooler that cools High pressure refrigerant discharged from the compressor. The expansion valve decompresses this from the cooler outflowing Refrigerant. The evaporator vaporizes the refrigerant flowing out of the expansion valve and passes the gas refrigerant to the compressor. The controller controls an opening degree of the expansion valve so that the refrigerant pressure on reaches a target pressure before decompression on a high-pressure side, which is selected from a first target pressure and a second target pressure. Of the first target pressure is an optimal pressure based on a Temperature of the cooler outflowing refrigerant is determined, and the second target pressure is lower than the first Target pressure. The controller sets the second target pressure as the target pressure for one predetermined time after the start of the compressor and sets the first target pressure as the target pressure after elapse of the predetermined time one.

Of the Refrigerant pressure will be immediately after the start of the compressor on the second Target pressure regulated. This prevents the refrigerant temperature from overflowing Limit temperature of the compressor increases. In addition, the refrigerant pressure after elapse of the predetermined time to the first target pressure regulated, whereby the refrigerant cycle device with the highest Efficiency is operated.

Alternatively, the target pressure is set to the second target pressure when an elapsed time after the start of the compressor is less than that before is certain time and a heat load state of a refrigerant circuit is determined as a high load state, and the target pressure is set to the first target pressure when the heat load state is determined as a low load state, even if the elapsed time is less than the predetermined time.

If the heat load condition the low load condition has the temperature of the compressor output refrigerant no way about that Limit temperature of the compressor to rise. Therefore, even if the refrigerant pressure immediately after the start of the compressor to the first set pressure is controlled, prevents the refrigerant temperature over the Limit temperature of the compressor increases. As a result, the Refrigerant circuit device immediately after the start of the compressor with the highest efficiency operate.

According to one Another aspect of the invention is a method for controlling a Refrigerant circuit device provided a compressor, a radiator and an expansion valve having. The procedure contains a step of determining whether an elapsed time after the Starting the compressor less than a predetermined time is one step for setting a first target pressure based on a temperature of the cooler outflowing Refrigerant so that an efficiency of a refrigerant circuit reaches a maximum value, a step of setting a second target pressure lower than the first target pressure, a step of controlling an opening degree of the expansion valve so that a refrigerant pressure before decompression achieved by the expansion valve, the second target pressure, if the elapsed time is less than the predetermined time, and a step of controlling the opening degree of the expansion valve so that the refrigerant pressure before decompression achieved by the expansion valve, the first target pressure when the elapsed time not less than the predetermined time determined becomes.

In The method is the refrigerant pressure on the second target pressure is controlled when the elapsed time is lower is determined as the predetermined time. This prevents that the refrigerant temperature immediately after the start of the compressor above the limit temperature of the compressor Compressor rises. Furthermore becomes the refrigerant pressure regulated to the first target pressure, if the elapsed time is not less than the predetermined time is determined. This can do that Process the refrigerant cycle device after elapse of the predetermined time with the highest efficiency Taxes.

alternative becomes the opening degree of the expansion valve controlled so that a refrigerant pressure before decompression achieved by the expansion valve, the second target pressure, if the elapsed time is determined lower than the predetermined time is and a heat load condition a refrigerant circuit as the high load state is determined, and becomes the opening degree of the expansion valve so controlled that the refrigerant pressure before the decompression by the expansion valve, the first target pressure achieved when the heat load condition is determined as the low load condition, even if the elapsed Time less than the predetermined time is determined.

If the heat load condition When the low load condition is determined, the temperature of the Compressor discharged refrigerant no way about that Rise to the limit temperature of the compressor. Therefore, even when the refrigerant pressure immediately after the start of the compressor to the first set pressure is controlled, prevents the refrigerant temperature over the Limit temperature of the compressor increases. As a result, the Process the refrigerant cycle device immediately control with the highest efficiency after starting the compressor.

Further Objects and advantages of the present invention will become apparent from the following detailed description of preferred embodiments better understood together with the accompanying drawings. Show:

1 a schematic representation of a refrigerant cycle device according to an embodiment of the invention;

2 FIG. 12 is a graph showing a relationship between a pressure of the refrigerant flowing out of a radiator and an efficiency (COP) of a refrigerant circuit corresponding to a refrigerant temperature; FIG.

3 a diagram of an example of temperature characteristics of a stationary target pressure P ₁ and a start-time target pressure P ₂ ;

4 a flowchart of an example of a control process of the refrigerant cycle device; and

5 FIG. 15 is a time chart showing a temperature of the refrigerant flowing out of a compressor when the refrigerant cycle device is controlled by methods according to an example of the embodiment (A), a first comparative example (B), and a second comparative example (C).

(Embodiments)

A refrigerant cycle device according to ei In an exemplary embodiment, reference is made to FIG 1 described. The refrigerant cycle device may be suitably used for air conditioning in a vehicle. For example, carbon dioxide (CO ₂ ) is used as the refrigerant circulating in a refrigerant circuit of the refrigerant cycle device. A pressure of CO ₂ on a high-pressure side before decompression may be set higher than a critical pressure of CO ₂ , that is, CO ₂ on a high-pressure side may be set in a supercritical state.

The refrigerant cycle device includes the refrigerant circuit and an electronic control unit (ECU) 10 , The refrigerant circuit contains a compressor 1 , a cooler 2 , an indoor heat exchanger 3 , an expansion valve 4 , an evaporation apparatus 5 and a memory 8th which are connected in a closed circuit.

The compressor 1 is for compressing the refrigerant in a supercritical state with a high temperature and a high pressure is provided. The compressor 1 has an electromagnetic clutch 1a , The compressor 1 may be a fixed-capacity type or a variable-capacity type provided by a vehicle engine (not shown) by the electromagnetic clutch 1a is driven. Alternatively, the compressor 1 to be an electric compressor.

The cooler 2 is a gas cooler for cooling the refrigerant and is on one side of an outlet of the compressor 1 arranged. The cooler 2 is a heat exchanger in which the compressor 1 Exhausted refrigerant exchanges heat with outside air to cool the refrigerant. An electric cooling fan 2a is for blowing outside air to the radiator 2 arranged.

The indoor heat exchanger 3 contains a high pressure side passage 3a and a low pressure side passage 3b , The high pressure side passage 3a is on one side of a refrigerant outlet of the radiator 2 arranged and the expansion valve 4 is on a side of a refrigerant outlet of the high-pressure side passage 3a arranged. The expansion valve 4 is an electric expansion valve in which an opening degree of the expansion valve 4 is electrically controlled so that a refrigerant pressure on the high pressure side reaches a target pressure.

In particular, the expansion valve contains 4 an electric actuator 4a with a stepper motor and a through the electric actuator 4a driven valve element 4b , An opening degree of the valve element 4b is according to an operating angle of the actuator 4a precisely controlled.

The evaporator 5 is on one side of a refrigerant outlet of the expansion valve 4 arranged. An air conditioning unit for the vehicle has a housing 6 defining an air passage through which air flows into a vehicle compartment. The evaporator 5 is in the case 6 for cooling the air in the housing 6 arranged.

An electric fan 7 is on an air upstream side of the evaporator 5 arranged. The fan 7 air introduced from an inside air / outside air change box (not shown) blows to the housing 6 so that the air passes through the evaporator 5 flows.

A heater core (not shown) is in the housing 6 disposed and is on a downstream air side of the evaporator 5 for heating the evaporator 5 arranged flowing air. A temperature of the air to be blown into the vehicle compartment is controlled by a heating degree of the heater core, and air conditioning air blows from at least one outlet of the housing 6 in the vehicle compartment.

The memory 8th is on a side of a refrigerant outlet of the evaporator 5 arranged. The memory 8th is a gas / liquid separator, in which the from the evaporator 5 escaping refrigerant in gas refrigerant and liquid refrigerant is separated. The memory 8th stores excess refrigerant in the refrigerant cycle device therein, and supplies the separated gas refrigerant to a refrigerant inlet of the compressor 1 out.

The low-pressure side passage 3b of the indoor heat exchanger 3 is on one side of a refrigerant outlet of the memory 8th arranged. An outlet pipe of the store 8th is with the refrigerant inlet of the compressor 1 through the low-pressure side passage 3a coupled.

In the heat exchanger 3 exchange this from the memory 8th outflowing low pressure gas refrigerant heat with the out of the cooler 2 outflowing high pressure refrigerant. This will increase the enthalpy of the evaporator 5 flowing refrigerant and a difference between the refrigerant enthalpy at a refrigerant inlet of the evaporator and a refrigerant enthalpy at the refrigerant outlet of the evaporator 5 will be raised. So a cooling capacity of the refrigerant circuit increases.

The ECU 10 for controlling the refrigerant circuit includes a microcomputer and a peripheral circuit. The ECU 10 performs predetermined arithmetic processing based on a predetermined program for controlling the elements the refrigerant cycle device (eg air conditioning element).

In particular, the climate elements such as the electromagnetic clutch 1a of the compressor 1 , the electric cooling fan 2a the radiator 2 , the expansion valve 4 and the fan 7 with an output side of the ECU 10 connected so that the ECU 10 controls the climate elements.

The refrigerant cycle device further includes a pressure sensor 12 , a refrigerant temperature sensor 13 , an evaporator temperature sensor 14 and an outside air temperature sensor 15 provided with an input page of the ECU 10 are connected.

For example, the pressure sensor 12 on the refrigerant outlet side of the radiator 2 for detecting a pressure of the from the radiator 2 outflowing refrigerant arranged as in 1 shown. Alternatively, the pressure sensor 12 also between the compressor 1 and the radiator 2 for detecting a pressure of the compressor 1 output refrigerant and the ECU 10 can cause a pressure drop in the radiator 2 estimated.

In addition, the ECU reads 10 Measurement signals from a group of sensors 16 for example, including an indoor temperature sensor, a solar radiation sensor, an engine cooling water temperature sensor. Furthermore, the ECU receives 10 Climate control signals from a climate control panel 17 , which is arranged for example next to an instrument panel in the vehicle compartment.

In particular, the ECU receives 10 the climate control signals including a temperature setting signal for setting a temperature in the vehicle compartment, an operation signal of the compressor 1 , an air volume change signal of the blower 7 , an outlet mode change signal of the air conditioning unit and an air inlet mode change signal of the inside air / outside air exchange box.

An operation of the refrigerant cycle device of the embodiment will now be described. First, a basic operation of the refrigerant cycle device will be described. If the ECU 10 an operating signal of the compressor 1 from the control of the climate panel 17 receives, the ECU performs 10 the electromagnetic clutch 1a Power too, so the electromagnetic clutch 1a enters a connection state. Thereby, a driving force of the vehicle engine by the electromagnetic clutch 1a on the compressor 1 transfer.

Then the compressor compresses 1 the refrigerant in a high temperature / high pressure state, whereby a refrigerant pressure is higher than a critical pressure, that is, the refrigerant enters the supercritical state. The supercritical refrigerant flows into the radiator 2 and exchanges heat with the one from the cooling fan 2a blowing outside air, whereby the supercritical refrigerant gives off heat to the outside air.

The refrigerant flows out of the radiator 2 through the high pressure side passage 3a of the indoor heat exchanger 3 to the expansion valve 4 , When the refrigerant passes through the high-pressure side passage 3a the refrigerant exchanges heat with the low-pressure refrigerant in the low-pressure side passage 3b out, which makes the cooler 2 escaping refrigerant gives off heat to the low-pressure refrigerant.

That through the high pressure side passage 3a flowing refrigerant flows to the expansion valve 4 and is through a throttle passage of the valve element 4b decompressed into a gas / liquid state with a low temperature and a low pressure. The gas / liquid refrigerant flows to the evaporator 5 and evaporates by absorbing heat from that through the blower 7 blown air. That's how the blower works 7 blown air through the evaporator 5 cooled and cooling air flows to the vehicle compartment.

The low pressure refrigerant from the evaporator 5 flows to the store 8th , The memory 8th separates the low-pressure refrigerant into a saturated liquid refrigerant and a saturated gas refrigerant, and supplies the saturated gas refrigerant to the compressor 1 out.

The low pressure gas refrigerant (ie, refrigerant drawn by the compressor) flows from the reservoir 8th to the low pressure side passage 3b and absorbs heat from the cooler 2 outflowing refrigerant. Thus, the enthalpy of the refrigerant sucked by the compressor increases and the refrigerant sucked by the compressor gets into a superheated state. The superheated refrigerant is passed through the compressor 1 sucked and compressed again.

The pressure of the cooler 2 effluent refrigerant can by controlling the opening degree of the expansion valve 4 be regulated so that the COP is maximized. In particular, as determined in 2 represented, the ECU 10 a target pressure P ₁ for optimal pressure control corresponding to a temperature of the cooler 2 escaping refrigerant, so that the COP is maximized.

When a through the pressure sensor 12 detected actual pressure P _{h is} higher than the target pressure P ₁ , the Opening degree of the expansion valve 4 elevated. On the other hand, when the actual pressure P _{h is} lower than the target pressure P ₁ , the opening degree of the expansion valve becomes 4 reduced.

Thus, the actual high pressure P _{h can be set} to the target pressure P ₁ for the optimum pressure control by controlling the opening degree of the expansion valve 4 be managed. Thereby, the COP is maximized and the refrigerant cycle device is operated efficiently.

The target pressure P ₁ for the optimum pressure control is a stationary target pressure P ₁ and becomes larger as the temperature of the refrigerant increases, as in FIG 3 shown. A start-time target pressure P ₂ is set lower than the stationary target pressure P ₁ .

A control process of the expansion valve 4 will now be referring to 4 described. The control process starts when the refrigerant cycle device is started and operated (ie, the compressor 1 is started).

First, step S1 reads the measurement signals from the sensors 12 - 16 and the climate control signals from the climate control panel 17 , Step S2 determines whether an elapsed time "t" after the start of the compressor 1 is less than a predetermined time t ₁ .

The predetermined time t ₁ may be, for example, 10 minutes. When step 2 determines that the elapsed time "t" is less than the predetermined time t ₁ (Y), step S2 determines that the refrigerant cycle device immediately after the start of the compressor 1 is in a transient state. Then, step S3 determines whether or not a heat load state of the refrigerant circuit is a high load state.

In particular, step S3 reads the measurement signals from the outside air temperature sensor 15 and determines whether or not the detected outside air temperature is not lower than a predetermined temperature (eg, about 35 ° C). If step S3 determines that the detected outside air temperature is not lower than the predetermined temperature, step S3 determines that the refrigerant cycle is in the high load state (Y), and step S4 sets the start time target pressure P ₂ as the target pressure.

On the other hand, when step S2 determines that the elapsed time "t" is not less than the predetermined time t ₁ (N), step S2 determines that the refrigerant cycle transits from the transient state to a steady state state, then step S5 sets the steady state target pressure P ₁ as the target pressure.

If step S3 determines that the refrigerant cycle is in the low-load state (N), step S5 sets the target stationary pressure P ₁ as the target pressure.

When the refrigerant cycle is in the high load state, step S6 controls the opening degree of the expansion valve 4 so that through the pressure sensor 12 detected actual pressure P _{h of} the refrigerant reaches the starting time target pressure P ₂ . That is, in step S6, a pressure reduction control is performed. In contrast, step S7 controls the opening degree of the expansion valve 4 so that the actual pressure P _{h reaches} the stationary target pressure P ₁ . That is, in step S7, an optimal pressure control is performed.

Specifically, when the actual pressure P _{h is} higher than the target pressure P ₁ or P ₂ , the opening degree of the expansion valve 4 increased. On the other hand, when the intake pressure P _{h is} lower than the target pressure P ₁ or P ₂ , the opening degree of the expansion valve becomes 4 reduced.

The stationary target pressure P ₁ is the refrigerant pressure determined according to the refrigerant temperature at which the COP is maximized, as in FIG 2 shown. Ie in 2 For example, in the pressure control line changed in accordance with the refrigerant temperature, an optimum refrigerant pressure at which the COP is maximized is used as the stationary target pressure P ₁ . When the heat load state of the refrigerant circuit changes and the refrigerant temperature changes, the optimum refrigerant pressure, which is set based on the refrigerant temperature, is used as the stationary target pressure P ₁ .

Therefore, when the refrigerant circuit is in the steady state, the opening degree of the expansion valve 4 controlled so that the actual pressure P _{h reaches} the stationary target pressure P ₁ . Therefore, the Istr pressure P _h is controlled so that the COP is constantly high, whereby the refrigerant cycle device is operated with the highest efficiency.

In contrast, the start-time target pressure P _{2 is set} lower than the stationary target pressure P ₁ , as in FIG 3 shown. Therefore, even if the refrigerant temperature changes, the start-time target pressure P _{2 is} always lower than the stationary target pressure P ₁ .

In an in 3 example shown is when the temperature of the cooler 2 escaping refrigerant increases, a difference between the stationary target pressure P ₁ and the start-time target pressure P ₂ greater. In addition, the start-time target pressure P _{2 is set} to a constant pressure (eg, about 12 MPa) when the temperature of the refrigerant is higher than a predetermined temperature (eg, about 60 ° C).

A temperature change of the Kom pressor 1 refrigerant discharged when the refrigerant cycle device is controlled by a method according to an example of the embodiment will now be described with reference to FIG 5 compared with cases in which the refrigerant cycle device is controlled by methods according to a first comparative example and a second comparative example, respectively.

In the example of the embodiment shown by line A, the ECU performs 10 the depressurization control using the start-time target pressure P ₂ for the predetermined time t ₁ (eg, about 10 minutes) after the start of the compressor 1 and performs the optimum pressure control using the steady state target pressure P ₁ after elapse of the predetermined time t ₁ .

In the first comparative example shown by the line B, the ECU controls 10 the refrigerant pressure immediately after the start of the compressor 1 to the stationary target pressure P ₁ .

In contrast, the ECU continues 10 in the second comparative example shown by the line C, a target pressure corresponding to the start-time target pressure P _2, and controls the refrigerant pressure immediately after the start of the compressor 1 to the low target pressure.

In the first comparative example (B), the temperature of the compressor 1 discharged refrigerant above a threshold temperature T _{L of} a structural element of the compressor 1 in the transition state immediately after the compressor start. This can ensure a durability of the compressor 1 be reduced. The limit temperature T _L is a durability of a non-metal element in the compressor 1 , eg a rubber element for sealing. In an example in 5 the limit temperature T _{L is} about 150 ° C.

In the second comparative example (C), the ECU performs 10 the depressurization control using the low target pressure in the transient state immediately after the start of the compressor 1 by, similar to the example of the embodiment. Therefore, it is prevented that the refrigerant temperature at the time immediately after the start of operation of the compressor 1 above the limit temperature T _L increases. However, in the second comparative example (C), the ECU keeps 10 the pressure reduction control even when the refrigerant circuit is in the steady state. Therefore, the refrigerant pressure is controlled to the low target pressure that is lower than an optimum pressure determined based on the COP (ie, the steady-state target pressure P ₁ ). Thereby, the COP of the refrigerant circuit in the steady state can be reduced and the refrigerant cycle device can be operated with a low efficiency.

In contrast, in the example (A) of the embodiment, the ECU performs 10 the depressurization control using the start-time target pressure P ₂ in the transient state immediately after the start of the compressor 1 by. This prevents the refrigerant temperature from rising above the threshold temperature T _L and reduces the durability of the compressor 1 is restricted.

In addition, in the example (A) of the embodiment, the ECU performs 10 the optimum pressure control using the steady state target pressure P ₁ , after the refrigerant circuit is changed to the steady state. Therefore, the ECU optimizes 10 the actual pressure P _h such that the COP is constantly maximized, whereby the refrigerant cycle device is operated with the highest efficiency.

Thus, in the example (A) of the embodiment, the refrigerant temperature is prevented from rising above the threshold temperature T _L when the refrigerant cycle device is in the transient state. In addition, the refrigerant cycle device is operated at the highest efficiency when the refrigerant cycle is in the steady state.

In the example of the embodiment, step S5 sets if step S3 in FIG 4 determines that the heat load state is low (N), the steady state target pressure P ₁ as the target pressure.

When the heat load condition is a low load condition, the temperature of the compressor is high 1 discharged refrigerant no way beyond the limit temperature T _{L of} the compressor 1 to rise. Therefore, the ECU performs 10 the optimal pressure control using the stationary target pressure P ₁ immediately after the start of the compressor 1 by. Thereby, the refrigerant cycle device becomes immediately after the start of the compressor 1 operated with the highest efficiency.

(Further embodiments)

Even though the present invention in conjunction with its preferred embodiments fully described with reference to the accompanying drawings has to be noted that various changes and modifications for the skilled person will be obvious.

For example, in the embodiment described above, step S3 determines the heat load state of the refrigerant circuit based only on the outside air temperature. Alternatively, step S3 may be the heat load condition of the refrigerant circuit based on a solar radiation amount and / or the Determine the temperature in the vehicle compartment in addition to the outside air temperature.

Alternatively, step S3 may be a measurement signal of the temperature of the compressor 1 discharged refrigerant from a temperature sensor and can calculate an increase rate of the temperature. The rate of increase of the temperature of the compressor 1 output refrigerant increases as the heat load becomes larger. Thus, step S3 may determine the heat load state based on the rate of increase of the refrigerant temperature instead of the outside air temperature.

In an in 3 As shown, the starting time set pressure P _{2 changes} according to the temperature of the radiator 2 outflowing refrigerant analogous to the stationary target pressure P ₁ . However, the start-time target pressure P _{2 is used} only in the depressurization control that is temporarily immediately after the start of the compressor 1 is carried out. Therefore, the start-time target pressure P _{2 may be} a predetermined fixed value.

In the control process in 4 Step S4 sets the start-time target pressure P _2, and Step S6 performs the pressure reduction control when Step S2 determines that the elapsed time "t" is less than the predetermined time t ₁ (Y), and Step S3 determines that the heat load state of The refrigerant circuit is the high load state (Y) Alternatively, step S3 may be omitted and the ECU 10 For example, the pressure decreasing control may be performed using the start-time target pressure P ₂ for the predetermined time t ₁ after the start of the compressor, and performs the optimum pressure control using the steady-state target pressure P ₁ after the lapse of the predetermined time t ₁ .

In this case, the ECU performs 10 the depressurization control using the start-time target pressure P ₂ in the transient state immediately after the start of the compressor 1 and performs the optimum pressure control using the stationary target pressure P ₁ after shifting the refrigerant circuit to the steady state. This prevents the refrigerant temperature from rising above the threshold temperature T _L when the refrigerant cycle is in the transient state. In addition, the refrigerant cycle device is operated at the highest efficiency when the refrigerant cycle is in the steady state.

In the embodiment described above, CO _{2 is used} as the refrigerant for the refrigerant cycle device. Alternatively, another refrigerant such as ethylene and ethane may be used for the refrigerant cycle device in which the refrigerant pressure may be increased to the critical pressure of the refrigerant or higher.

in the Embodiment described above the refrigerant cycle device used for example for air conditioning in the vehicle. Alternatively, you can the refrigerant cycle device also for a house or the like can be used.

Such changes and modifications are of course within the scope of the present invention as defined by the appended claims is.

Claims (13)

Refrigerant cycle device, with a compressor ( 1 ) for compressing a refrigerant higher than a critical pressure of the refrigerant; a cooler ( 2 ) for cooling the compressor ( 1 ) discharged high-pressure refrigerant; an expansion valve ( 4 ) for decompressing the from the cooler ( 2 ) discharged refrigerant; an evaporator ( 5 ) for vaporizing the from the expansion valve ( 4 ) flowing refrigerant and passing the gas refrigerant to the compressor ( 1 ); and a controller ( 10 ) for controlling an opening degree of the expansion valve ( 4 ) such that the refrigerant pressure on a high pressure side before decompression reaches a target pressure selected from a first target pressure (P ₁ ) and a second target pressure (P ₂ ), the first target pressure (P ₁ ) being an optimum pressure based on a temperature of the cooler ( 2 ) is determined, and the second target pressure (P ₂ ) is lower than the first target pressure (P ₁ ), wherein the controller ( 10 ) for a predetermined time (t ₁ ) after the start of the compressor ( 1 ) sets the second target pressure (P ₂ ) as the target pressure and, after elapse of the predetermined time (t ₁ ), sets the first target pressure (P ₁ ) as the target pressure. Refrigerant cycle device according to claim 1, further comprising a determination device ( 10 ) for determining a heat load condition of a refrigerant circuit, wherein the controller ( 10 ) sets the second target pressure (P ₂ ) as the target pressure when an elapsed time (t) after the start of the compressor ( 1 ) is less than the predetermined time (t ₁ ) and the determining device ( 10 ) determines that the heat load condition of the refrigerant circuit is a high load state; and the controller ( 10 ) changes the setpoint pressure to the first setpoint pressure (P ₁ ) if the determination device ( 10 ) determines that the heat load condition is a low load condition even if the elapsed time (t) is less than the predetermined time (t ₁ ). Refrigerant cycle device according to claim 2, in which the determining device ( 10 ) the heat load state based on an outside air temperature determined. Refrigerant cycle device according to claim 2, in which the determining device ( 10 ) the heat load state based on an increase rate of a temperature of the compressor ( 1 ) discharged refrigerant after the start of the compressor ( 1 ) certainly. The refrigerant cycle device according to any one of claims 1 to 4, wherein the second target pressure (P ₂ ) is based on a temperature of the refrigerant from a refrigerant outlet of the radiator (P ₂ ). 2 ) flowing refrigerant is determined. The refrigerant cycle device according to any one of claims 1 to 4, wherein the second target pressure (P ₂ ) is set to a predetermined fixed value. Refrigerant cycle device according to one of claims 1 to 6, wherein the first set pressure (P ₁ ) is determined so that an efficiency of a refrigerant circuit reaches a maximum value. Method for controlling a refrigerant cycle device comprising a compressor ( 1 ), a cooler ( 2 ) and an expansion valve ( 4 ), the method comprising: determining (S2) whether an elapsed time (t) after the start of the compressor ( 1 ) is less than a predetermined time (t ₁ ); Adjusting (S5) a first target pressure (P ₁ ) based on a temperature of the cooler ( 2 ) flowing refrigerant so that an efficiency of a refrigerant circuit reaches a maximum value; Setting (S4) a second target pressure (P ₂ ) lower than the first target pressure (P ₁ ); Controlling (S6) an opening degree of the expansion valve (FIG. 4 ) such that a refrigerant pressure before decompression by the expansion valve ( 4 ) reaches the second target pressure (P ₂ ) when the elapsed time (t) is determined to be less than the predetermined time (t ₁ ); and controlling (S7) the opening degree of the expansion valve (FIG. 4 ) such that the refrigerant pressure before decompression by the expansion valve ( 4 ) reaches the first target pressure (P1) when the elapsed time (t) is not less than the predetermined time (t ₁ ). The method of claim 8, further comprising determining (S3) if a heat load condition is a high load condition, wherein the opening degree of the expansion valve is ( 4 ) is controlled so that a refrigerant pressure before the decompression by the expansion valve ( 4 ) reaches the second target pressure (P ₂ ) when the elapsed time (t) is determined to be less than the predetermined time (t ₁ ) and the heat load condition is determined to be the high load condition; and the degree of opening of the expansion valve ( 4 ) is controlled so that the refrigerant pressure before the decompression by the expansion valve ( 4 ) reaches the first target pressure (P ₁ ) when the heat load condition is determined to be a low load condition even if the elapsed time (t) is determined to be less than the predetermined time (t ₁ ). The method of claim 9, wherein the heat load condition based on an outside air temperature is determined. The method of claim 9, wherein the heat load condition is based on an increase rate of a temperature of the compressor ( 1 ) discharged refrigerant after the start of the compressor ( 1 ) is determined. The refrigerant cycle device according to any one of claims 8 to 11, wherein the second target pressure (P ₂ ) is determined based on a temperature of the refrigerant from a refrigerant outlet of the radiator (P ₂ ). 2 ) flowing refrigerant is determined. A refrigerant cycle device according to any one of claims 8 to 11, wherein the second target pressure (P ₂ ) is set to a predetermined fixed value.