Air conditioning system

An air conditioning system, including a condenser for condensing a refrigerant, a first expansion device for throttling the refrigerant passed through the condenser, a second expansion device for throttling the refrigerant passed through the first expansion device, an evaporator for evaporating the refrigerant passed through the second expansion device, a compressor for compressing the refrigerant passed through the evaporator and the refrigerant injected after branched between the first expansion device and the second expansion device, and a control unit for detecting a value of at least one operating parameter and determining a target opening degree of the first expansion device on the basis of a stored set value corresponding to the detected value of the operating parameter.

This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 10-2008-0000217 filed in Republic of Korea on Jan. 2, 2008 and No. 10-2008-0000218 filed on Jan. 2, 2008, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to an air conditioning system, and more particularly, to an air conditioning system, which can improve the performance and stability of the system.

2. Discussion of the Related Art

Generally, an air conditioning system is a device for cooling or heating an indoor space by performing compression, condensation, expansion and evaporation of a refrigerant.

The air conditioning systems are classified into a normal air conditioner including an outdoor unit and an indoor unit connected to the outdoor unit and a multi-type air conditioner including an outdoor unit and a plurality of indoor units connected to the outdoor unit. Moreover, the air conditioning systems are classified into a cooling air conditioner supplying a cool air only to an indoor space by driving a refrigerant cycle in one direction only and a cooling and heating air conditioner supplying a cool or hot air to an indoor space by driving a refrigerant cycle selectively and bi-directionally.

The air conditioning system includes a compressor, a condenser, an expansion valve, and an evaporator. The refrigerant discharged from the compressor is condensed in the condenser, and then expands in the expansion valve. The expanded refrigerant is evaporated in the evaporator, and then sucked into the compressor. IN a cooling operation or heating operation, a gaseous refrigerant is injected into the compressor, thus improving performance.

However, the air conditioning system according to the related art has the problem that the system may become unstable and damage to the compressor or the like may occur if not controlled properly.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an air conditioning system, which can improve the performance and stability of the system.

The present invention provides an air conditioning system, comprising: a condenser for condensing a refrigerant; a first expansion device for throttling the refrigerant passed through the condenser; a second expansion device for throttling the refrigerant passed through the first expansion device; an evaporator for evaporating the refrigerant passed through the second expansion device; a compressor for compressing the refrigerant passed through the evaporator and the refrigerant injected after between the first expansion device and the second expansion device; and a control unit for detecting a value of at least one operating parameter and determining a target opening degree of the first expansion device on the basis of a stored set value corresponding to the detected value of the operating parameter.

In the present invention, the compressor includes: a first compressing part for compressing the refrigerant passed through the evaporator; and a second compressing part for compressing the refrigerant passed through the first compressing part and the refrigerant injected after branched between the first expansion device and the second expansion device.

In the present invention, the at least one operating parameter may be a plurality of operating parameters, and the plurality of operating parameters may change the target opening degree of the first expansion device independently. The target opening degree of the first expansion device may be determined based on a linear combination of the set values for the operating parameters. Also, the target opening degree of the first expansion device may be determined based on a multiplied value of the set values for the operating parameters.

In the present invention, the set values of some of the operating parameters may be differently set according to the operability of gas injection in which a refrigerant is branched between the first expansion device and the second expansion device and injected into the compressor. The operating parameters include the frequency of the compressor, the indoor temperature and outdoor temperature of the air conditioning system, and the operability of gas injection in which a refrigerant is branched between the first expansion device and the second expansion device and injected into the compressor.

In accordance with another aspect of the present invention, there is provided an air conditioning system, comprising: a condenser for condensing a refrigerant; a first expansion device for throttling the refrigerant passed through the condenser; a second expansion device for throttling the refrigerant passed through the first expansion device; an evaporator for evaporating the refrigerant passed through the second expansion device; a compressor for compressing the refrigerant passed through the evaporator and the refrigerant injected after branched between the first expansion device and the second expansion device; and a control unit for detecting a value of at least one operating parameter and determining a target opening degree of the first expansion device on the basis of a stored set value corresponding to the detected value of the operating parameter and controlling such that a change in opening degree may change according to the opening time of the first expansion device until the opening degree of the first expansion device reaches the target opening degree.

In the present invention, the control unit may perform a change process of changing the opening amount of the first expansion device until the opening degree of the first expansion device reaches the target opening degree and a maintenance process of maintaining a changed opening degree. In at least some of the change process, a change in opening degree may be controlled so as to be changed according to opening time, and in the maintenance process, an opening degree maintenance time may be controlled so as to be changed according to the change in opening degree. The change in opening degree may be preset depending on the difference between the target opening degree and the current opening degree, and the opening amount of the first expansion valve may be controlled based on a combined value of the current opening degree and the change in opening degree. The change in opening degree may be preset so as to be proportional to the difference between the target opening degree and the present opening degree.

In accordance with still another aspect of the present invention, there is provided an air conditioning system, comprising: a condenser for condensing a refrigerant; a first expansion device for throttling the refrigerant passed through the condenser; a second expansion device for throttling the refrigerant passed through the first expansion device; an evaporator for evaporating the refrigerant passed through the second expansion device; a compressor for compressing the refrigerant passed through the evaporator and the refrigerant branched and injected between the first expansion device and the second expansion device; and a control unit for controlling the first expansion device in a first control method and the second expansion device in a second control method different from the first control method.

In the present invention, the compressor includes: a first compressing part for compressing the refrigerant passed through the evaporator; and a second compressing part for compressing the refrigerant passed through the first compressing part and the refrigerant injected by being branched between the first expansion device and the second expansion device.

In the present invention, in the first control method, a value of at least one operating parameter may be detected, and a target opening degree of the first expansion device may be determined on the basis of a stored set value corresponding to the detected value of the operating parameter.

In the present invention, in the second control method, the degree of superheat of the refrigerant may be measured in real time, and the opening degree of the second expansion device may be changed based on the measured degree of superheat until the measured degree of superheat reaches a preset degree of superheat.

In the present invention, the control unit may control the first expansion device in the first control method, and if a value of at least one operating parameter is out of a preset normal operating range, the control unit may control the first expansion device by switching to a safety control method which is different from the first control method. In the first control method, the current opening degree of the first expansion device may be stored in real time, and in the safety control method, the opening amount of the first expansion device may be controlled on the basis of the current opening degree stored in the first control method upon switching from the first control method. In the safety control method, a correction opening degree may be determined based on the operating parameter value, and the opening amount of the first expansion device may be controlled by combining the correction opening degree with the current opening degree stored in the first control method upon switching from the first control method.

In the present invention, if the degree of superheat of the refrigerant is within a preset range of a target degree of superheat, the control unit may perform fuzzy control over the opening amount of the first expansion device by switching from the first control method.

To accomplish the above object of the air conditioning system of the present invention, the first expansion device and the second expansion device playing a different role from each other are controlled in a different control method suitable for each role, thereby improving the performance and stability of the system.

Furthermore, in the present invention, the control method for the first expansion device is differentiated according to the operation state of the air conditioning system, thereby improving the stability of the system.

Furthermore, in the present invention, the intermediate pressure can be adjusted more rapidly and precisely according to the state of the air conditioning system by differentiating the control method for the first expansion device for adjusting the intermediate pressure depending on the degree of superheat of the refrigerant, thereby improving the stability and performance of the system.

Furthermore, in the present invention, the first expansion device is gradually opened by controlling such that a change in opening degree may change according to the opening time of the first expansion device, thereby improving the stability of the system and achieving more stable switching of the control method for the first expansion device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An air conditioning system includes general residential cooling air conditioner for performing a cooling operation only, a heating air conditioner for performing a heating operation only, a heat pump type air conditioner for performing both cooling and heating operations, and a multi-type air conditioner for cooling and heating a plurality of indoor spaces. Hereinafter, as one example of the air conditioning system, a heat pump type air conditioner (hereinafter, referred to as “air conditioner”) will be described in details.

Hereinafter, embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1is a view showing the construction of an air conditioner100in accordance with a first embodiment of the present invention.FIG. 2is a block diagram showing a control flow of the air conditioner100.

Referring toFIGS. 1 and 2, the air conditioner100includes a compressor110, an indoor heat exchanger120, an outdoor heat exchanger130, a first expansion valve141, a second expansion valve142, a phase separator150, and a 4-way valve160. The indoor heat exchanger120functions as an evaporator in a cooling operation and functions as a condenser in a heating operation. The compressor110compresses an introduced refrigerant of low temperature and low pressure into a refrigerant of high temperature and high pressure. The compressor110includes a first compressing part111and a second compressing part112. The first compressing part111compresses the refrigerant introduced from the evaporator, and the second compressing part112mixes and compresses the refrigerant coming from the first compressing part111and the refrigerant injected by being branched between the evaporator and the condenser. However, the present invention is not limited thereto, and the compressor110can have a multi-layered structure more than three layers.

The 4-way valve160is a flow path switching valve for switching the flow of refrigerant upon cooling and heating, and guides the refrigerant compressed in the compressor110to the outdoor heat exchanger130upon cooling and guides the same to the indoor heat exchanger120upon heating. The 4-way valve160and the compressor110are connected via a first connecting pipe171. A compressor outlet temperature sensor181and a discharge pressure sensor182are disposed on the first connecting pipe171in order to measure the discharge temperature and pressure of the refrigerant discharged from the compressor110. The indoor heat exchanger120is disposed in a room, and is connected to the 4-way vale160via a second connecting pipe172.

The phase separator150separates an introduced refrigerant into a gaseous refrigerant and a liquid refrigerant, sends the liquid refrigerant to the evaporator, and sends the gaseous refrigerant to the second compressing part112. A first connecting part151of the phase separator150and the indoor heat exchanger120are connected via a third connecting pipe173. The first connecting part151serves as a liquid refrigerant discharge pipe in a cooling operation and serves as a refrigerant inlet pipe in a heating operation.

The first expansion valve141is disposed on the third connecting pipe173, and serves as a second expansion device for throttling the liquid refrigerant introduced from the phase separator150in a cooling operation and serves as a first expansion device for throttling the liquid refrigerant introduced from the indoor heat exchanger120in a heating operation.

The outdoor heat exchanger130is disposed outdoors, and is connected to a second connecting part152of the phase separator150via a fourth connecting pipe174. The second connecting pipe152serves as a refrigerant inlet pipe in a cooling operation and serves as a liquid refrigerant discharge pipe in a heating operation.

The second expansion valve142is disposed on the fourth connecting pipe174, and serves as a first expansion device for throttling the liquid refrigerant introduced from the heat exchanger130in a cooling operation and serves as a second expansion device for throttling the liquid refrigerant introduced from the phase separator150in a heating operation.

The outdoor heat exchanger130is connected to the four-way valve160via a fifth connecting pipe175. Also, the 4-way valve160and an inlet pipe of the compressor110are connected via a sixth connecting pipe176. A compressor inlet temperature sensor184for measuring the temperature of the inlet side of the compressor110is disposed on the sixth connecting pipe176.

The second compressing part112is connected to a third connecting part153of the phase separator150via an injection pipe180. The third connecting pipe153is used as a gaseous refrigerant discharge pipe in cooling and heating operations. An injection valve143is disposed on the injection pipe180. The injection valve143controls the amount and pressure of the refrigerant injected into the second compressing part112from the phase separator150. When the injection pipe180is opened, the gaseous refrigerant in the phase separator150is introduced into the second compressing part112through the injection pipe180. An injection temperature sensor183for measuring the temperature of the refrigerant being injected is disposed on the injection pipe180.

The opening degree of the first and second expansion valves141and142and the injection valve143is controlled by a control unit200for controlling the operation of the air conditioner.

FIG. 3illustrates the flow of refrigerant in the heating operation of the air conditioner.

Referring toFIG. 3, a gaseous refrigerant of high temperature and high pressure discharged from the compressor110is introduced into the indoor heat exchanger120via the 4-way valve160. In the indoor heat exchanger120, the gaseous refrigerant is condensed by heat exchange with indoor air. The condensed refrigerant is throttled in the first expansion valve141, and then introduced into the phase separator150. The liquid refrigerant separated by the phase separator150is throttled again in the second expansion valve142, and then introduced into the outdoor heat exchanger130. The refrigerant in the outdoor heat exchanger130is evaporated by heat exchange with ambient air, and the evaporated refrigerant is introduced into the first compressing part111.

If there is a request for performing gas injection during the heating operation, the control unit200opens the injection valve143. As the injection valve143is opened, the gaseous refrigerant separated from the phase separator150is injected into the second compressing part112through the injection pipe180. In the second compressing part112, the injected refrigerant and the refrigerant coming from the first compressing part111are mixed and then compressed. The refrigerant compressed in the second compressing part112circulates again to the 4-way valve160.

FIG. 4illustrates the flow of refrigerant in the cooling operation of the air conditioner.

Referring toFIG. 4, a gaseous refrigerant of high temperature and high pressure discharged from the compressor110is introduced into the outdoor heat exchanger130via the 4-way valve160. In the outdoor heat exchanger130, the gaseous refrigerant is condensed by heat exchange with indoor air. The condensed refrigerant is throttled in the second expansion valve142, and then introduced into the phase separator150. The liquid refrigerant separated by the phase separator150is throttled again in the first expansion valve141, and then introduced into the indoor heat exchanger120. The refrigerant in the indoor heat exchanger120is evaporated by heat exchange with ambient air, and the evaporated refrigerant is introduced into the first compressing part111.

If there is no request for performing gas injection during the cooling operation, the control unit200closes the injection valve143, thus keeping the gaseous refrigerant coming from the phase separator150from being injected into the second compressing part112. However, the present invention is not limited thereto, and in the cooling operation, too, the gaseous refrigerant coming from the phase separator150may be injected into the second compressing part112.

FIG. 5is a sequential view illustrating a method of controlling first and second expansion valves of an air conditioner as shown inFIG. 1.

Referring toFIG. 5, a method of controlling an air conditioner in accordance with the first embodiment of the present invention will be described below.

If a user drives the air conditioner100in order to cool and heat an indoor space, the control unit200detects a driving command.

When the driving command is detected, the control unit200initializes the first and second expansion valves141and142and the injection valve143. (S1). That is to say, the control unit200fully opens the first and second expansion valves141and142, and closes the injection valve143. By closing the injection valve143, a liquid refrigerant can be kept from being introduced into the compressor110at an initial stage of driving.

Once the initialization of the first and second expansion valves and the injection valve143is finished, the control unit200adjusts the degree of superheat so that the refrigerant of the air conditioner100may reach a preset target degree of superheat. Further, the refrigerant is adapted to reach a preset intermediate pressure.

Here, the degree of superheat is the difference between the temperature of the refrigerant sucked into the compressor110and the saturation temperature with respect to the evaporating pressure of the evaporator. The degree of superheat can be measured by a sensor installed in the evaporator and a compressor inlet temperature sensor184installed at the inlet side of the compressor. As the sensor installed in the evaporator, an outdoor heat exchanger sensor186installed in the outdoor heat exchanger130is used upon heating, and an indoor heat exchanger sensor185installed in the indoor heat exchanger120is used upon heating.

The intermediate pressure is a pressure in the phase separator150. By adapting the intermediate pressure to reach a preset intermediate pressure, the work required by the compressor110can be reduced, thus increasing efficiency. By adjusting the amount of the refrigerant supplied to the phase separator150from the condenser, the intermediate pressure can be adjusted. The intermediate pressure can be calculated from the temperature measured by the injection temperature sensor183installed in the injection pipe180.

The control unit200adjusts the opening degree of the valve disposed between the phase separator150and the evaporator in order to adjust the degree of superheat. Also, the control unit200adjusts the opening degree of the valve disposed between the condenser and the phase separator150in order to adjust the intermediate pressure.

The control unit200controls the valve for adjusting the intermediate pressure of the refrigerant and the valve for adjusting the degree of superheat of the refrigerant in different control methods. In other words, the control unit200controls the opening degree of the valve in a first control method in order to adjust the intermediate pressure, and controls the opening degree of the valve in a second control method different from the first control method in order to adjust the degree of superheat or the like of the refrigerant.

Referring toFIG. 5, the control unit200checks whether the air conditioner100is in a heating operation mode or in a cooling operation mode, and selects the method of controlling the first expansion valve141and the second expansion valve142between the first and second methods. (S2)

First, the method of controlling the first and second expansion valves141and142when the air conditioner100is in the heating operation mode will be described below.

If the air conditioner100is in the heating operation mode, the control unit200controls the first expansion valve141in the first control method, and controls the second expansion valve142in the second control method. (S3)

If the air conditioner100is in the heating operation mode, the first expansion valve141throttles the refrigerant introduced into the phase separator150after condensed in the indoor heat exchanger120. At this time, it is possible to make the pressure in the phase separator150reach a preset intermediate pressure by adjusting the opening degree of the first expansion valve141. Therefore, the control unit200controls the first expansion valve141in the first control method.

Further, the second expansion valve142throttles the refrigerant coming from the phase separator150and introduced into the outdoor heat exchanger130. The degree of superheat of the refrigerant can be adjusted by adjusting the opening degree of the second expansion valve142. Therefore, the control unit200controls the second expansion valve142in the second control method.

FIG. 6is a sequential view illustrating a first control method for the first expansion valve when the air conditioner as shown inFIG. 1is in a heating operation mode.

Referring toFIG. 6, in the first control method (S10), when the initialization of the first expansion valve141is finished (S1), a value of at least one operating parameter is detected (S11), and a stored set value corresponding to the detected value of the operating parameter is calculated (S12). A target opening degree of the valve is determined based on the set value (S13). The target opening degree of the first expansion valve141is determined based on the set value. The operating parameters may include the operability of gas injection in which refrigerant is injected into the second compressing part112, the frequency of the compressor110, the indoor temperature of the air conditioner100, an outdoor temperature, the difference between the indoor and outdoor temperatures, the discharge pressure of the compressor110, the discharge temperature of the compressor110, etc. The set values for the operating parameters are preset and stored in a table format in the control unit200. The set value for the frequency of the compressor110may be set differently according to the operability of gas injection.

The set values for the operating parameters change the target opening degree independently. A subsequent method of obtaining the target opening degree is as follows:

In one example, the target opening degree can be obtained by multiplying the set values corresponding to the operating parameters values by each other, and the following equation can be used:
F(A1,A2,A3,A4,A5, . . . )=C*f(A1)*(A2)*(A3)*(A4)*f(A5)*

Since the operating parameters change the target opening degree of the first expansion valve141independently, it is easy to obtain a set value for each operating parameter and it is easy to control.

As above, once the opening degree of the first expansion valve141is determined, the control unit200increases or decreases the opening degree until the opening degree of the first expansion valve141reaches the target opening degree. (S14)

Accordingly, the intermediate pressure of the refrigerant can reach a preset intermediate pressure more rapidly.

Meanwhile, the second control method is a method of measuring the degree of superheat of the refrigerant until the degree of superheat of the refrigerant reaches a target degree of superheat and controlling the opening degree of the valve based on the measured degree of superheat. The degree of superheat of the refrigerant can be measured by the outdoor heat exchanger sensor186installed in the outdoor heat exchanger130serving as an evaporator in a heating operation and the compressor indoor temperature sensor184. A fuzzy table is stored in the control unit200on the basis of a difference between a measured degree of superheat and a preset target degree of superheat and a change in difference, and the opening degree of the second expansion valve142is determined from the fuzzy table.

As above, the opening degree of the second expansion valve142continually changes on the basis of the degree of superheat that is measured in real time, and thus the degree of superheat of the refrigerant can be adjusted more precisely according to the operation state of the air conditioner100.

On the other hand, a method of controlling the first and second expansion valves141and142when the air conditioner100is in a cooling operation mode will be described below.

If the air conditioner100is in the cooling operation mode, the control unit200controls the first expansion valve141in the second control method for adjusting the degree of superheat, and controls the second expansion valve142in the first control method for adjusting the intermediate pressure (S4).

If the air conditioner100is in the cooling operation mode, the first expansion valve141throttles the refrigerant coming from the phase separator150and introduced into the indoor heat exchanger120. Thus, the degree of superheat of the refrigerant can be adjusted by adjusting the opening degree of the first expansion valve141. Therefore, the control unit200controls the first expansion valve141in the second control method.

As the first expansion valve141is controlled in the second control method, the opening a degree of the first expansion valve141continually changes on the basis of the degree of superheat that is measured in real time. Therefore, the degree of superheat of the refrigerant can be adjusted more precisely.

Further, the second expansion valve142throttles the refrigerant introduced into the phase separator150after condensed in the outdoor heat exchanger130. Thus, it is possible to make the pressure in the phase separator150reach a preset intermediate pressure by adjusting the opening amount of the second expansion valve142. Therefore, the control unit200controls the second expansion valve142in the first control method S10.

As the second expansion valve142is controlled in the first control method S10, the target opening degree of the second expansion valve142is set on the basis of a stored set value corresponding to the detected value of the operating parameter. The opening amount of the second expansion valve142decreases or increases at a time until the opening degree of the second expansion valve142reaches the target opening degree. Therefore, the intermediate pressure of the refrigerant can be adjusted more rapidly.

In the present invention, the first expansion valve141is controlled in the first control method S10if the air conditioner100is in the heating operation mode, while the first expansion valve141is controlled in the second control method if the air conditioner100is in the cooling operation mode. In contrast, the second expansion valve141is controlled in the second control method if the air conditioner100is in the heating operation mode, while the second expansion valve142is controlled in the first control method S10if the air conditioner100is in the heating operation mode. Hence, the roles of the first and second expansion valves141and142become different depending on the cooling and heating operation modes of the air conditioner100and, accordingly, the control method becomes different, thereby improving the performance and stability of the system.

Meanwhile, it is checked whether there is a request for performing gas injection regardless of the cooling and heating operation modes (S5).

If there is a request for performing gas injection, the control unit200opens the injection valve143. On the other hand, if there is no request for performing gas injection, the control unit200closes the injection valve143(S7).

Alternatively, in a second embodiment, which is different from the first embodiment, the target opening degree can be obtained by the following equation. The following description focuses on these differences with the foregoing embodiment.

In other words, the target opening degree can be obtained by adding the set values to each other. In the above equation, the target opening degree is obtained by linearly combining the set values, thus making easier the control of the first expansion device over each of the set values.

Alternatively, in a third embodiment, which is different from the previous embodiments, the target opening degree can be obtained by the following equation. Hereinafter, description will be made with respect to the differences with the foregoing embodiment.

In the above equation, the actual characteristics of the operating parameter values can be expressed by using various constants (f1, f2, f3. . . ), thus improving the accuracy of control.

Hereinafter, a control method for first and second expansion valves of an air conditioner in accordance with a fourth embodiment of the present invention will be described. The following description focuses on the difference with the first embodiment. The same reference numerals as those in the first embodiment denote the same members.

The difference with the first embodiment is that the control unit200controls the first expansion device in a different control method according to the operation state of the air conditioner. That is to say, the control unit200selects any one of the first control method S20and a safety control method S30, and controls the first expansion device.

If the air conditioner is in a heating operation, the first expansion valve141serves as the first expansion device for adjusting the intermediate pressure and the second expansion valve142serves as the second expansion device for adjusting the degree of superheat.

FIG. 7is a sequential view illustrating a control method for a first expansion valve when an air conditioner according to a fourth embodiment of the present invention is in a heating operation mode.

Referring toFIG. 7, when the initialization of the first expansion valve141is finished (S1), the control unit200adjusts the opening amount of the first expansion valve141in order to adjust the intermediate pressure. At this time, the control unit200selects any one of the first control method S20and the safety control method S30according to the operation state of the air conditioner100, and controls the first expansion valve141. That is, the control unit200judges whether the air conditioner100is in a normal operation state, and switches the control method for the first expansion valve141according to the result. If the operating parameter value is within a preset normal operating range, the control unit200judges the air conditioner to be in the normal operation state, and controls the first expansion valve141in the first control method S20. Otherwise, if the operating parameter value is out of the preset normal operating range, the control method for the first expansion valve141is switched to the safety control method S30which is different from the first control method S20.

The control unit200detects the operating parameters, such as the discharge temperature of the refrigerant discharged from the compressor110and the temperature of the refrigerant passed through the indoor heat exchangers120serving as a condenser in a heating operation. If the detected values of the operating parameters are out of a preset normal range, the control unit200judges that there may be problems like liquid compression, and thus the control unit200switches to the safety control method S30which is capable of preventing liquid compression or the like.

First, if the operating parameter values are within the preset normal operating range, the air conditioner100is judged to be in a normal operation state and the first control method S20is performed.

In the first control method S20, a value of the operating parameter is detected (S21), and a stored set value corresponding to the detected value of the operating parameter is calculated (S22). Based on the set value, a target opening degree of the first expansion valve is determined (S23). Once the target opening degree is determined, the opening amount is increased or decreased at a time so that the opening degree of the first expansion valve141may reach the target opening degree (S24). Therefore, the intermediate pressure of the refrigerant can reach a preset intermediate pressure more rapidly.

The control unit200stores the current opening degree of the first expansion valve141during the execution of the first control method S20(S25). The current opening degree stored in the first control method S20is used upon switching from the first control method S20to the safety control method S30.

During the execution of the first control method S20, the control unit200detects whether the operating parameters, such as the discharge temperature of the refrigerant discharged from the compressor110and the temperature of the refrigerant passed through the indoor heat exchangers120, are out of a preset normal operating range (S26). If the operating parameters, such as the discharge temperature of the refrigerant discharged from the compressor110and the temperature of the refrigerant passed through the indoor heat exchangers120, are out of a preset normal operating range, the control unit200switches from the first control method S20to the safety control method S30.

The control unit200measures a refrigerant discharge temperature of the compressor110in order to get the discharge temperature of the refrigerant discharged from the compressor110and prevent liquid compression. If the measured refrigerant discharge temperature is out of a preset normal operating range and lower than a preset temperature, the control unit200switches from the first control method S20to the safety control method S30. The normal operating range is preset and stored in the control unit200according to the operating condition or the like of the air conditioner.

When the first control method S20is switched to the safety control method S30, the current opening degree stored during the execution of the first control method S20is combined with a correction opening degree in the safety control method S30(S32). The correction opening degree may be determined based on the refrigerant discharge temperature (S31). The opening amount of the first expansion valve141is controlled according to the combined value of the current opening degree and the correction opening degree (S33). That is to say, the opening amount of the first expansion valve141can be increased by adding the correction opening degree to the current opening degree, or the opening amount of the first expansion valve141can be decreased by subtracting the correction opening degree from the current opening degree.

During the execution of the safety control method S30, the current opening degree of the first expansion valve141is stored in real time (S34). Therefore, during the execution of the safety control method S30, the current opening degree stored during the execution of the safety control method S30is combined with the correction opening degree.

The safety control method S30is a method of opening or closing as much as the correction opening degree from the current opening degree stored. That is, the opening degree of the first expansion valve141is gradually reduced by the correction opening degree until the refrigerant discharge temperature of the compressor110is higher than a preset temperature. As the opening degree of the first expansion valve141is reduced, the amount of the refrigerant is reduced, thus making it possible to ensure the refrigerant discharge temperature of the compressor110. Accordingly, liquid compression in the compressor110can be prevented.

Meanwhile, if the refrigerant discharge temperature of the compressor110returns to the normal operating range during the execution of the safety control method S30, the control unit200switches from the safety control method S30to the first control method S20to control the opening amount of the first expansion valve141.

If the refrigerant discharge temperature of the compressor110is within a preset normal operating range, the control unit200measures the temperature of the refrigerant coming from the indoor heat exchanger120. If the temperature of the refrigerant passed through the indoor heat exchanger120is out of the preset normal operating range and lower than a preset temperature, the control unit200switches from the first control method S20to the safety control method S30. Upon switching from the first control method S20to the safety control method S30, in the safety control method S30, a correction opening degree is determined based on the temperature of the refrigerant passed through the indoor heat exchanger120, and the correction opening degree is combined with the current opening degree. Then, the opening amount of the first expansion valve141is controlled according to the combined value thereof. Afterwards, the current opening degree of the first expansion valve141is stored in real time during the execution of the safety control method S30, and the correction opening degree is combined with the current opening degree stored during the execution of the safety control method S30. The opening degree of the first expansion valve141is gradually increased by the correction opening degree until the temperature of the refrigerant passed through the indoor heat exchanger120is higher than a preset temperature. By increasing the opening degree of the first expansion valve141, the temperature of the outlet side of the indoor heat exchanger120can be increased.

If the temperature of the refrigerant passed through the indoor heat exchanger returns to a temperature higher than the preset temperature, the control unit200switches from the safety control method S30to the first control method S20to control the opening amount of the first expansion valve141.

Further, if the temperature of the refrigerant passed through the indoor heat exchanger120is within a preset normal operating range, the discharge temperature of the compressor110is measured in order to prevent the discharge temperature of the compressor110from being excessively increased. If the discharge temperature of the compressor110is out of the normal operating range and exceeds a preset temperature, the control unit200switches from the first control method S20to the safety control method S30. In the safety control method S30, the correction opening degree is combined with the opening degree of the first expansion valve141stored during the execution of the first control method S20to control the opening amount of the first expansion valve141. Afterwards, the current opening degree of the first expansion valve141is stored in real time during the execution of the safety control method S30, and the correction opening degree is combined with the opening degree stored during the execution of the safety control method S30. The opening degree of the first expansion valve141is gradually increased by the correction opening degree until the discharge temperature of the compressor110is lower than a preset temperature. By increasing the opening degree of the first expansion valve141, the discharge temperature of the compressor110can be prevented from being increased. Accordingly, damage of the compressor110can be prevented.

If the refrigerant discharge temperature of the compressor110is dropped to lower than a preset temperature, the control unit200switches from the safety control method S30to the first control method S20to control the opening amount of the first expansion valve141.

In the first control method S20, a target opening degree is set regardless of the current opening degree of the first expansion valve141, and the target opening degree is reached at a time. Therefore, if the air conditioner is in a normal operation state, more rapid control can be performed compared to the controlling of the first expansion valve141in the first control method S20.

On the other hand, in the safety control method S30, the opening degree of the first expansion valve141is gradually decreased or gradually increased. Therefore, if the air conditioner100is not in a normal operation state, the opening amount of the first expansion valve141is controlled more precisely according to the operation state, thereby making it easier to return to the normal operation state.

Meanwhile, the control unit200controls the opening amount of the second expansion valve142so that the degree of superheat can reach a preset target degree of superheat. The control unit200is able to control the opening amount of the second expansion valve142by correcting the target degree of superheat in order to ensure the discharge temperature of the compressor110after the initialization of the second expansion valve142. That is to say, after the initialization of the second expansion valve142, if the discharge temperature of the compressor110is lower than a preset temperature, the control unit200can set a new target degree of superheat by correcting the preset target degree of superheat by a predetermined value, and accordingly can control the opening amount of the second expansion valve142. Therefore, after the initialization of the second expansion valve142, the discharge temperature of the compressor110can be ensured.

Afterwards, if the discharge temperature of the compressor10is higher than a preset temperature, the control unit200can control the opening amount of the second expansion valve142so as to reach a preset target degree of superheat.

Meanwhile, in a cooling operation, the second expansion valve142serves as the first expansion device for adjusting the intermediate pressure and the first expansion valve142serves as the second expansion device for adjusting the degree of superheat.

Accordingly, in the cooing operation, one of the first control method S20and the safety control method S30is selected to control the second expansion valve142according to the operation state. That is, if an operating parameter value is within a normal operating range, the second expansion valve142is controlled in the first control method S20, while, if the operating parameter value is out of the normal operating range, the first control method S20is switched to the safety control method S30to control the opening amount of the second expansion valve142.

In other words, if the refrigerant discharge temperature of the compressor110is out of the normal operating range and is lower than a preset temperature, the first control method S20is switched to the safety control method S30. In the safety control method S30, a correction opening degree is determined according to the refrigerant discharge temperature. And, the opening degree of the second expansion valve142is gradually reduced by the correction opening degree until the refrigerant discharge temperature is higher than the preset temperature. As the second expansion valve142is gradually closed, the refrigerant discharge temperature of the compressor110cab be ensured.

Further, the temperature of the inlet side of the indoor heat exchanger120serving as the evaporator is out of the normal operating range and is lower than a preset temperature, the first control method S20is switched to the safety control method S30. In the safety control method S30, a correction opening degree is determined according to the temperature of the inlet side of the indoor heat exchanger S30. And, the opening degree of the second expansion valve142is gradually increased by the correction opening degree until the temperature of the inlet side of the indoor heat exchanger120is within the normal operating range. Therefore, pipelines at the inlet side of the indoor heat exchanger120can be prevented from freezing.

Further, if the discharge temperature of the compressor110is out of the normal operating range and exceeds a preset temperature, the first control method S20is switched to the safety control method S30. In the safety control method S30, a correction opening degree is determined according to the discharge temperature of the compressor110. And, the opening degree of the second expansion valve142is gradually increased by the correction opening degree until the discharge temperature of the compressor110is lower than the preset temperature. Therefore, the discharge temperature of the compressor110can be prevented from being excessively increased.

Also, when the air conditioner100is in overload, a preset target degree of superheat is corrected by a predetermined value to set a new target degree of superheat, and accordingly the opening amount of the first expansion valve141can be controlled. Therefore, it is possible to cope with the overload of the air conditioner100.

Hereinafter, a control method for first and second expansion valves of an air conditioner in accordance with a fifth embodiment of the present invention will be described. The following description focuses on the difference with the first embodiment. The same reference numerals as those in the first embodiment denote the same members.

The difference with the first embodiment is that the control unit200uses a plurality of different control methods in order to adjust the intermediate pressure. That is to say, the control unit200determines a control method for the first expansion device for adjusting the intermediate pressure by comparing the degree of superheat of the refrigerant with a preset range of a target degree of superheat. The range of the target degree of superheat is a range of a target degree of superheat, which can be preset by an experiment or the like, and in which the cycle of the air conditioner can be stabilized. The control unit200determines a control method by comparing the degree of superheat of the refrigerant with the range of the target degree of superheat and accordingly judging whether the cycle is stabilized or not. In other words, if the degree of superheat of the refrigerant is out of the range of target degree of superheat, the first expansion device is controlled in the first control method S10, and if the degree of superheat of the refrigerant is within a preset range of a target degree of superheat, the first expansion device is controlled in a fuzzy control method S40which is switched from the first control method S10.

First, if the air conditioner is in a heating operation, the first expansion valve141serves as the first expansion device for adjusting the intermediate pressure, and the second expansion valve142serves as the second expansion device for adjusting the degree of superheat.

FIG. 8is a sequential view illustrating a control method for a first expansion valve when an air conditioner in accordance with a fifth embodiment of the present invention is in a heating operation mode.

Referring toFIG. 8, the control unit200initializes the first expansion valve141, and then adjusts the opening amount of the first expansion valve141in order to adjust the intermediate pressure. At this time, the control unit200selects any one of the first control method S10and the fuzzy control method S40according to the degree of superheat of the refrigerant to control the first expansion valve141.

It is checked whether the degree of superheat of the refrigerant is out of the range of the target degree of superheat or not (S410). If the degree of superheat of the refrigerant is out of the range of the target degree of superheat, the control unit200controls the first expansion valve141in a first control method S10. In the first control method S10, a value of the operating parameter is detected (S11), and a stored set value corresponding to the detected value of the operating parameter is calculated (S12). Based on the set value, a target opening degree of the first expansion valve is determined (S13). Once the target opening degree is determined, the opening amount is increased or decreased at a time so that the opening degree of the first expansion valve141may reach the target opening degree (S14, S15). Therefore, the intermediate pressure of the refrigerant can reach a preset intermediate pressure more rapidly. Details of the first control method S10are the same as those in the first embodiment, so they will be omitted.

Meanwhile, if the degree of superheat of the refrigerant is within a preset range of a target degree of superheat, the control unit200judges that the cycle of the air conditioner enters a stabilization step. Accordingly, the control unit200controls the first expansion valve141in the fuzzy control method S40in order to match the intermediate of the refrigerant with a preset intermediate pressure more precisely.

In the control unit200, a fuzzy table is stored according to an operating parameter value. In the fuzzy control method S40, an operating parameter value is measured, and the opening amount of the first expansion valve141is fuzzy-controlled according to the fuzzy table. Here, the operating parameter value will be explained by way of example of the pressure of the injection pipe180. The opening amount of the first expansion valve141is continually changed until the pressure of the injection pipe180reaches a preset intermediate pressure. The pressure of the injection pipe180can be ensured by measuring a temperature from the injection temperature sensor183installed in the injection pipe180and converting the measured injection temperature into a pressure (S42). A fuzzy table is stored in the control unit200based on the injection temperature. On the basis of the fuzzy table, the control unit200calculates the opening amount of the first expansion valve141(S43), and changes the opening amount of the first expansion valve141(S44). Afterwards, the opening amount of the first expansion valve141is feedback-controlled until the injection pressure reaches the target intermediate pressure (S45).

Accordingly, the first control method S10is a method in which the target opening degree of the first expansion valve141is determined and the opening amount of the first expansion valve141is opened or increased at a time until the current opening degree of the first expansion valve141reaches the target opening degree. The fuzzy control method S40is a method of gradually changing the opening amount of the first expansion valve141according to the injection temperature or pressure. That is, in the fuzzy control method40, the opening amount of the first expansion valve141is finely adjusted compared to the first control method S10.

Accordingly, if the degree of superheat of the refrigerant is out of the range of the target degree of superheat, the opening amount of the first expansion valve141can be adjusted to a greater extent by using the first control method S10. If the degree of superheat of the refrigerant is within the range of the target degree of superheat, the opening amount of the first expansion valve141is finely adjusted by using the fuzzy control method S40, thereby matching the intermediate pressure of the refrigerant with a preset intermediate pressure more precisely.

Meanwhile, if the air conditioner is in a cooling operation mode, the second expansion valve142serves as the first expansion device for adjusting the intermediate pressure, and the first expansion valve141serves as the second expansion device for adjusting the degree of superheat.

Accordingly, in the cooing operation, one of the first control method S10and the fuzzy control method S40is selected to control the second expansion valve142according to the operation state. That is, if the degree of superheat of the refrigerant is out of the range of the target degree of superheat, the second expansion valve142is controlled in the first control method S10, while, if the degree of superheat of the refrigerant is within the range of the target degree of superheat, the second expansion valve142is controlled in the fuzzy control method S40.

Hereinafter, a control method for first and second expansion valves of an air conditioner in accordance with a sixth embodiment of the present invention will be described. The following description focuses on the difference with the first embodiment. The same reference numerals as those in the first embodiment denote the same members.

The difference with the first embodiment is that, in a first control method S50for controlling the first expansion device for adjusting the intermediate pressure, the control unit200controls such that a target opening degree of the first expansion device may be determined and then a change in opening degree may change according to the opening time of the first expansion device until the opening degree of the first expansion device reaches the target opening degree.

First, if the air conditioner is in a heating operation, the first expansion valve141serves as the first expansion device for adjusting the intermediate pressure, and the second expansion valve142serves as the second expansion device for adjusting the degree of superheat.

FIG. 9is a sequential view illustrating a control method for a first expansion valve when an air conditioner in accordance with a sixth embodiment of the present invention is in a heating operation mode.

Referring toFIG. 9, the control unit200controls the opening amount of the first expansion valve141in a first control method S50in order to adjust the intermediate pressure after finishing the initialization of the first expansion valve141. In the first control method S50, it is controlled such that a target opening degree of the first expansion valve141is determined, and then a change in opening degree changes according to the opening time of the first expansion valve141until the opening degree of the first expansion valve141reaches the target opening degree.

In the first control method S50, a value of at least one operating parameter is detected (S51). The control unit200can obtain set values for the operating parameter value from the table (S52). A target opening degree of the first expansion valve is determined based on the set values (S53). The target opening degree can be obtained by a combination of the set values.

Next, the control unit200detects and stores the current opening degree of the first expansion vale141in real time (S54). The stored current opening degree and the target opening degree are compared with each other (S55). If the current opening degree and the target opening degree are different from each other, a change in opening degree is determined depending on the difference between the current opening degree and the target opening degree. The change in opening degree is preset depending on the difference between the current opening degree and the target opening degree. The change in opening degree is stored in a table format in the control unit200. Therefore, the control unit200obtains the difference between the current opening degree and the target opening degree, and obtains the change in opening degree from the table (S56).

Once the change in opening degree is determined, the opening degree of the first expansion valve141is changed by the change in opening degree (S57).

The control unit200continually detects the current opening degree of the first expansion valve141(S54). Then, the current opening degree of the first expansion valve141and the target opening degree are compared with each other again (S55). If the current opening degree and the target opening degree are different, the difference is calculated, and a change in opening degree is determined again depending on the difference (S56). If the change in opening degree is determined again, the opening degree of the first expansion valve is changed by the change in opening degree that has been determined again (S57).

The above-described process is repeated until the current opening degree of the first expansion valve is consistent with the target opening degree or within an error range.

FIG. 10is a graph showing a change in opening degree according to the opening time of the first expansion valve in accordance with the sixth embodiment of the present invention.

Referring toFIG. 10, the change in opening degree B1, B2, and B3may be set so as to be proportional to the difference between the current opening degree and the target opening degree. That is, because the difference between the current opening degree and the target opening degree is large at the initial stage of the control of the opening amount of the expansion valve141, the change in opening degree according to the opening time is increased, thus achieving more rapid control. Thereafter, the closer the opening degree of the first expansion valve reaches to the target opening degree, the smaller the change in opening degree according to the opening time becomes, thereby achieving more precise control.

Accordingly, in the first control method S50in accordance with the fourth embodiment of the present invention, the change in opening degree B1, B2, and B3are determined in consideration of the current opening degree of the first expansion valve, and the opening amount of the first expansion valve141is controlled a plurality of times until the current opening degree of the first expansion valve141reaches the target opening degree, thus gradually increasing or decreasing the opening degree of the first expansion valve141. In other words, since amount of the refrigerant gradually increases or decreases, the cycle can be more stabilized.

Meanwhile, if the air conditioner100is out of a normal operating range, the control unit200switches from the first control method S50to the safety control method S60to control the first expansion valve141.

In the safety control method S60, it is detected whether operating parameters, such as the discharge temperature of the refrigerant discharged from the compressor110and the temperature of the refrigerant passed through the indoor heat exchangers120, are out of a preset normal operating range (S61).

If the operating parameters, such as the discharge temperature of the refrigerant discharged from the compressor110and the temperature of the refrigerant passed through the indoor heat exchangers120, are out of a preset normal operating range, the control unit200switches from the first control method S50to the safety control method S60to control the first expansion valve141.

In the safety control method S60, a correction opening degree is determined based on the operating parameter values (S62), and the correction opening degree is combined with the opening degree stored in the first control method S50(S63) to control the opening amount of the first expansion valve141(S64). Afterwards, during the execution of the safety control method S60, the current opening degree of the first expansion valve141is stored in real time (S65), and the correction opening degree is combined with the current opening degree stored during the execution of the safety control method S60to control the opening amount of the first expansion valve141.

Accordingly, if the operating parameter value of the air conditioner10is out of the normal operating range, the control method for the first expansion valve141is switched to another method, thereby improving the stability of the system.

Moreover, in the first control method S50, the current opening degree of the first expansion valve141is detected and stored, and the opening degree of the first expansion valve141is gradually increased or decreased, thus making it easier to switch to another control method during the execution of the first control method141.

FIG. 11is a sequential view illustrating a first control method for a first expansion valve when an air conditioner in accordance with a seventh embodiment of the present invention is in a cooling operation mode. The following description focuses on the difference with the sixth embodiment. The same reference numerals as those in the sixth embodiment denote the same members.

The differences with the sixth embodiment include a change process in which the control unit200changes the opening degree of the first expansion valve141until the opening degree of the first expansion device reaches a target opening degree and a maintenance process in which the control unit200maintains a changed opening degree. In other words, when a change in opening degree is determined depending on the difference between the target opening degree and the current opening degree, the opening degree is changed by the change in opening degree (S71). Thereafter, the control of the first expansion valve141is stopped, and the opening degree of the first expansion valve141is maintained for a predetermined time (S72). The cycle can be more stabilized upon control of the first expansion valve by having the time for changing the opening degree and then maintaining the opening degree.

The change process S71and the maintenance process S72may be performed a plurality of times until the current opening degree of the first expansion valve141reaches the target opening degree.

FIG. 12is a graph showing a change in opening degree according to the opening time of the first expansion valve in accordance with the seventh embodiment of the present invention.

In one example, referring toFIG. 12, the change process S71and the maintenance process S72are each carried out three times. In the plurality of times of the change process, a change in opening C1, C2, and C3is controlled so as to be proportional to opening time. That is, because the difference between the current opening degree and the target opening degree is large at the initial stage of the control of the opening amount of the expansion valve141, the change in opening degree according to the opening time is increased, thus achieving more rapid control. Thereafter, as the opening time increases and the opening degree of the first expansion valve reaches closer to the target opening degree, the smaller the change in opening degree becomes smaller, thereby achieving more precise control. Also, an opening degree maintenance time T1, T2, and T3in the plurality of times of the maintenance process is controlled so as to be proportional to opening time. That is, the opening degree maintenance time is set to be long at the initial stage of the opening amount of the first expansion valve141. Thereafter, as the opening time gradually increases, the opening degree maintenance time T1, T2, and T3becomes smaller. Moreover, the opening degree maintenance time T1, T2, and T3may be set so as to be proportional to the change in opening degree C1, C2, and C3in the change process. Accordingly, the larger the change in opening degree of the first expansion valve141, the longer the opening degree maintenance time T1, T2, and T3, thereby further stabilizing the cycle upon control of the first expansion valve141.

Although the present invention has been described with reference to the embodiments shown in the drawings, these are merely illustrative, and those skilled in the art will understand that various modifications and equivalent other embodiments of the present invention are possible. Consequently, the true technical protective scope of the present invention must be determined based on the technical spirit of the appended claims.