GB2305744A

GB2305744A - Valve controller

Info

Publication number: GB2305744A
Application number: GB9620363A
Authority: GB
Inventors: Ichiro Hongo; Masakazu Andou
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1995-09-29
Filing date: 1996-09-27
Publication date: 1997-04-16
Anticipated expiration: 2016-09-27
Also published as: CN1140730C; GB9620363D0; JP3461633B2; JPH0996452A; KR970016383A; GB2305744B; KR100234347B1; CN1156810A; TW363119B

Abstract

In an air conditioner having a refrigerating cycle including a closable motor-operated expansion valve 5, the air conditioner control unit limits a variation quantity of the valve opening to a predetermined value or under when the current valve opening is less than a predetermined opening. Preferably the variation in opening of the valve is only limited when the valve is being closed.

Description

AIR CONDITIONER BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an air conditioner for controlling a refrigerating cycle while changing a coolant throttle quantity by use of a closable motor-operated expansion valve.

Related Background Art A motor-operated expansion valve has a wide using range. FIG. 11 is a sectional view schematically illustrating a construction of the motor-operated expansion valve. Referring to FIG. 11, a valve body 51 includes coolant ports 49, 50 formed downward and sideways, and includes a female screw 52 formed upward and meshing with a driving shaft 53. The driving shaft 53 has a male screw 54 formed in a middle portion. The driving shaft 53 also has an inward edge portion protruding inwardly of the valve body 51 and an outward edge portion protruding outwardly of the valve body 51. A valve rod 56 movable in an axial direction is so inserted as to be depressed downward by a spring 55 into the inward edge portion of the driving shaft. A front end of the valve rod 56 is formed with a needle 57 kept in contact with a valve seat 48 of the lower port 49 of the valve body 51.On the other hand, a permanent magnet 58 constituting a revolving-field pole of a pulse motor is fitted to an upper edge peripheral portion of the driving shaft 53. A stator 47 of the pulse motor is wound with a coil 59 acting on the permanent magnet 58.

The driving shaft 53 is rotated by applying driving pulses to the coil 59. A rotational motion of the driving shaft 53 is converted into an axial motion by the screws 52, 54, and the valve is opening and closed by separating the needle 57 from the valve seat 48 and bringing the needle 57 into contact therewith.

Note that the motor-operated expansion valve shown in FIG. 11 is moved downward in FIG. 11 by rotating the driving shaft 53, and the needle of the valve rod 56 contacts the valve seat. Thereafter, only the driving shaft 53 moves while the spring 55 is compressed. Then, the permanent magnet 58 stops in such a state as to impinge upon a stopper 60. The mechanism being thus constructed, an angle of rotation of the driving shaft 53 and a point at which the needle 57 separates from the valve seat 48, i.e., a valve opening point are different for every motoroperated expansion valve.

FIG. 12 is a diagram showing a relationship between a valve opening of the typical motor-operated expansion valve and a coolant flow rate, wherein when the valve opening is expressed by the number of driving pulses applied from a completely-closed position thereof, there are shown a Max flow rate level at which the flow rate is maximized for the same valve opening, a Min flow rate level at which the flow rate is minimized, and a Mean flow rate level at which the flow rate becomes mean. In this case, the valve opening is controllable up to 500 pulses, and therefore the using range is wide.

There is a scatter in terms of the valve opening for producing the flow rate in the vicinity of the completely closed state, i.e., a valve opening point, and hence it is required that the valve be used so as not to completely close the valve by giving a limit to the using range of for the valve opening. For this reason, the opening must be set by use of the motor-operated expansion valve having a small valve aperture to secure the coolant minimum flow rate.

As described above, when using the motor-operated expansion valve with the small valve aperture, the flow rate on the fully open side is restrained small, and the maximum flow rate in the refrigerating cycle is limited, resulting in such a problem that the variable using range is narrowed.

Further, if the motor-operated expansion valve is feedback-controlled without considering the fact that there is the scatter in the valve opening for producing the flow rate in the vicinity of the completely closed state, cycle clogging (which is the completely closed state of the motor-operated expansion valve) might occur, and an air conditioning capability of the air conditioner can not be controlled. Besides, there arise problems in which lubricating deterioration is caused due to the fact that a refrigerating machine oil discharged from a compressor is not returned to the compressor, and the compressor comes to have an abnormally high temperature because of a noncirculation of a coolant gas exhibiting a cooling effect for the compressor, thus causing a decline in reliability on the refrigerating cycle.

On the other hand, if a low flow rate is needed, as shown in FIG. 13A, a two-way valve 31 is connected in series to the motor-operated expansion valve 5, and further a capillary 32 for bypass is connected to the two-way valve 31. The two-way valve 31 is opened when controlling the flow rate but is closed during a low flow rate period.

Alternatively, as shown in FIG. 13B, the bypass capillary 32 is connected to the motor-operated expansion valve 5.

Such a construction, however, might bring about an increases in costs for the apparatus due to an addition of the parts and an increase in size of the outdoor unit.

SUMMARY OF THE INVENTION It is a primary object of the present invention, which was contrived to obviate the problems given above, to provide an air conditioner including a control unit capable of eliminating a possibility of causing a completely closed state during small flow rate control of a coolant in even a motor-operated expansion valve with a scatter in terms of a valve opening point in the vicinity of the completely closed state.

To accomplish the above object, an air conditioner according to the present invention comprises a control unit for limiting a variation quantity of the valve opening to a predetermined value or under when a valve opening is under a predetermined opening. The possibility of being completely closed during the small flow rate control of the coolant is thereby eliminated in even the motor-operated expansion valve with the scatter in terms of the valve opening point in the vicinity of the completely closed state.

The control unit ca be made effective only when the valve opening is changed in a closing direction. The possibility of being completely closed during the small flow rate control of the coolant can be thereby eliminated, and at the same time it is feasible to reduce a time of reaching an optimum opening corresponding to such a degree that no limit is given to an opening increment quantity.

An air conditioner according to the present invention comprises a control unit for limiting a variation quantity of a valve opening to a predetermined value or under when the valve opening is under a predetermined opening during super-heat-control, and for limiting the variation quantity of the valve opening to the predetermined value or under only when the valve opening is under the predetermined opening and when the valve opening is changed in a closing direction during the control of the motor-operated expansion valve on the basis of a change in capability of the compressor. There are exhibited effects, wherein the possibility of being completely closed during the small flow rate control of the coolant can be thereby eliminated, and at the same time it is possible to correspond to such a case that the capability of the compressor is changed largely.

Further, an air conditioner according to the present invention comprises a valve opening limiting unit for limiting a decrement quantity of a valve opening to a predetermined value or under when the valve opening of the motor-operated expansion valve is controlled in a closing direction after controlling at first the valve opening in an opening direction since the valve opening decreased under a predetermined opening on the occasion of superheat-controlling the valve opening of the motor-operated expansion valve at an interval of a predetermined time.

The possibility of being completely closed during the small flow rate control f the coolant can be thereby eliminated, and simultaneously a time of reaching an optimum opening can be reduced.

The air conditioner including the above valve opening limiting unit may further comprise a second valve opening limiting unit for limiting the increment quantity of the valve opening when thereafter controlling once again the valve opening of the motor-operated expansion valve in the opening direction. The possibility of being completely closed during the small flow rate control of the coolant can be thereby eliminated, and simultaneously the time of reaching the optimum opening can be further reduced.

Moreover, the air conditioner according to the present invention may further comprise a valve opening holding means for temporarily holding the valve opening of the motor-operated expansion valve to a predetermined opening when the valve opening is reduced under the predetermined opening from a position with a valve opening larger than the predetermined opening. Critical control can be executed by preventing control hunting.

Furthermore, the air conditioner according to the present invention may further comprise an initial opening control unit for fixing the opening of the motor-operated expansion valve to an opening larger than the predetermined opening when starting an operation. Stable control can be thereby attained with an output of a temperature sensor in a state where the condition of the refrigerating cycle is stabilized.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent during the following discussion in conjunction with the accompanying drawings, in which: FIG. 1 is a flowchart showing whole processing procedures of an outdoor microcomputer constituting one embodiment of the present invention; FIG. 2 is a refrigerating cycle system showing a construction of one embodiment of the present invention; FIG. 3 is a block diagram showing a signal input/output status of the outdoor microcomputer constituting one embodiment of the present invention; FIG. 4 is a flowchart showing a part of detailed processing procedures of the outdoor microcomputer constituting one embodiment of the present invention;; FIG. 5 is a flowchart showing a part of the detailed processing procedures of the outdoor microcomputer constituting one embodiment of the present invention; FIG. 6 is a flowchart showing a part of the detailed processing procedures of the outdoor microcomputer constituting one embodiment of the present invention; FIG. 7 is a flowchart showing a part of detailed processing procedures of the outdoor microcomputer constituting one embodiment of the present invention; FIG. 8 is a flowchart showing a part of the detailed processing procedures of the outdoor microcomputer constituting one embodiment of the present invention;; FIG. 9 is a flowchart showing a part of the detailed processing procedures of the outdoor microcomputer constituting one embodiment of the present invention FIG. lOA is a diagram, showing a relationship between a valve opening and a time, of assistance in explaining an operation of one embodiment of the present invention.

FIG. lOB is a diagram, showing a relationship between the valve opening and the time, of assistance in explaining an operation of a prior art; FIG. 11 is a sectional view illustrating a configuration of a general motor-operated expansion valve adopted in an air conditioner; FIG. 12 is a diagram showing a relationship between valve flow rates and openings of a variety of motor operated expansion valve adopted in the air conditioner; FIG. 13A is a diagram illustrating the motor-operated expansion valve to which a two-way valve and a capillary are added for preventing cycle clogging of the air conditioner; and FIG. 13B is a diagram illustrating the motor-operated expansion valve to which the capillary is added for preventing the cycle clogging of the air conditioner.

DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will hereinafter be described in detail.

FIG. 2 is a view of a refrigerating cycle system, illustrating a construction of one embodiment of the present invention. Referring to FIG. 2, the numeral 1 designates a compressor, and a well-known refrigerating cycle is constructed of a four-way valve 2, an indoor heat exchanger 3 having an indoor fan 4, a motor-operated expansion vale 5, capillary tubes 6a, 6b, and an outdoor heat exchanger 7 having an outdoor fan 8. Among the above components, the indoor unit 10 houses the indoor heat exchanger 3 and the indoor fan 4, while the outdoor unit 20 houses the compressor 1, the four-way valve 2, the motor-operated expansion valve 5, the capillary tubes 6a, 6b, the outdoor heat exchanger 7 and the outdoor fan 8.

Provided for controlling the compressor 1 and the motor-operated expansion valve 5 are an temperature sensor 9a for detecting a coolant temperature TE on an inlet side of the outdoor heat exchanger 7, a temperature sensor 9b for detecting an outside air temperature T,, a temperature sensor 9c for detecting a coolant temperature Ts on a suction side of the compressor 1, a temperature sensor 9d for detecting an indoor heat exchanger temperature Tc, and a temperature sensor 9e for detecting an indoor temperature Ta Output signals of these temperature sensor are, as shown in FIG. 3, supplied to an indoor microcomputer 11 and an outdoor microcomputer 21 provided in the outdoor unit 20. The indoor microcomputer 11 and the outdoor microcomputer 21 transmit and receive detected values to and from each other.Further, the indoor microcomputer 11 calculates a power supply frequency (hereinafter termed a compressor frequency" ) for driving the compressor 1.

Then, the indoor microcomputer 11 transmits a compressor frequency signal to the outdoor microcomputer 21 and also transmits an operation mode signal set by a remote control device or the like to the outdoor microcomputer 21.

Moreover, the indoor microcomputer 11 controls a velocity of an indoor fan motor. On the other hand, the outdoor microcomputer 21 controls an opening of the motor-operated expansion valve 5 by calculating the number of driving pulses of the motor-operated expansion value 5 and controls a velocity of the compressor 1 in accordance with the compressor frequency signal. The outdoor microcomputer 21 also controls energizing of the four-way valve 2 and further controls a velocity of an outdoor dan motor.

Among the variety of control operations, the calculation of the compressor frequency, the velocity control of the indoor fan motor, and the control operations of the velocities of the compressor and the outdoor fan motor have already proposed and well known. Therefore, explanations thereof are omitted, and the control of the opening of the motor-operated expansion valve 5 will hereinafter be explained.

To start with, the outdoor microcomputer 21, when controlling the opening of the motor-operated expansion vale 5, calculates the number of driving pulses so that a super heat quantity of the refrigerating cycle is equalized to a set value determined by an operating condition. In general, the super heat quantity is defined by a difference between the coolant temperature T on the suction side of the compressor 1 and the temperature of the heat exchanger used as an evaporator, i.e., the temperature Te of the outdoor heat exchanger 7 in this embodiment. However, an outlet-side temperature of the motor-operated expansion valve 5 is used as a temperature of the evaporator.

Further, a temperature difference between an indoor auxiliary heat exchanger and a main heat exchanger may be defined as a super heat quantity in the air conditioner for dehumidifying by employing a part of the indoor heat exchanger 3 as an evaporator. The super heat control is, however, nothing but to control the opening of the motoroperated expansion valve 5 so that the super heat quantity is equalized to the set value determined by the operating condition.

FIG. 1 is a flowchart showing specific processing procedures of the outdoor microcomputer 21 in connection with the super heat control. Herein, when started base don an operation command in step 101, the motor-operated expansion valve 5 receives 540 pulses and thereby fully opened in step 102. The valve opening of the motoroperated expansion valve 5 is controlled by the number of pulses. However, the number of pulses corresponding to the full-opening is, as obvious from FIG. 12, 500. Accordingly, if it is assumed that 540 pulses are applied in a closing direction, the motor-operated expansion valve 5 can be completely closed from any degree of valve opening at the starting point. Then, in step 103, the valve is set to an initial opening A shown in FIG. 12 by applying 60 pulses in an opening direction.This initial opening A is an opening for securing a flow rate higher than a minimum flow rate needed in the refrigerating cycle even if there might be a scatter in terms of valve opening point depending on flow rate levels. Then, the compressor is actuated in next step 104. Further in step 105, the valve is held in a state of the initial opening for three minutes, and there is awaited till the state of the coolant in the refrigerating cycle is stabilized.

Then, after three minutes have elapsed, an adjustment of the valve opening is started in step 106. At this time, the microcomputer calculates the number of pulses so that the super heat quantity is equalized to the set value, and the calculated number of pulses are applied to the motoroperated expansion valve 5. In this case, after controlling the valve opening, there might be a time-lag till reaction actually appears in the temperature sensor, and hence the number of output pulses to the motor-operated expansion valve 5 is calculated at an interval of a fixed control time TM, and then outputted. Note that the opening is required to be corrected corresponding to the compressor frequency under the super heat control, and there might be a possibility of being brought into an over-throttle state corresponding to the operating condition.Therefore, it is required that the opening be corrected for preventing that state. Then, when the compressor frequency changes during the operation, the number of pulses for correcting the opening is calculated corresponding to the change in the compressor frequency by an interrupt process in step 310. In the case of detecting the over-throttle state due to heating in the refrigerating cycle from the detected position of the temperature sensor 9c or 9d, the number of pulses for correcting the opening is calculated so as to obviate the over-throttle state by the interrupt process in step 320, i.e., to prevent the intermediate heating.

In the process of step 106, the number of pulses is properly selected in consideration of the number of pulses for correcting the opening. If, e.g., the indoor temperature Ta is coincident with a set room temperature during the above opening control, the compressor is controlled to stop. Then, if the compressor is stopped corresponding to the output of the temperature sensor, the valve is held with a predetermined opening corresponding to the stopped state of the compressor in step 109, and the processing from step 103 onward is executed. Then, for example, if a command to stop the operation is given from the remote controller during the operation, a full-open position is set in step 107, i.e., a 500-pulse opening is set, and the control is finished by cutting off the power supply in step 108.

Next, the detailed process in step 106 will be explained with reference to FIGS. 4 through 9.

Supposing that a variation quantity of the valve opening that is converted into the number of pulses is calculated and outputted as it is in such a state that the valve opening approximates to the initial opening A in FIG.

12 during the super heat control, there must be a possibility in which cycle clogging happens. FIG. 4 shows the processing procedures when the variation quantity of the valve opening controlled at the interval of a predetermined time is restricted under a predetermined value and then outputted. In this case, a variation quantity APLS1 (positive on the opening side but negative on the closing side) under the super heat control is calculated in first step 201. Then, a variation quantity APLS2 (positive on the opening side but negative on the closing side) for changing the compressor frequency and/or preventing the over-throttle state is calculated by the interrupt process in step 202. A variation quantity APLS of the valve opening is calculated by adding the above quantities in step 203.Then, in next step 205, a limit opening determined in a position that is somewhat larger than the initial opening A shown in FIG. 12, is compared with a present opening. If the present opening is smaller than the limit opening, the operation proceeds to a process in step 205, wherein a magnitude of the variation quantity APLS is limited. That is, if the variation quantity APLS is larger than a limit value APLSMM ( > 0) predetermined on the valve opening side, the variation quantity APLS is limited to the limit value APES, i.e., APLS = APLS.

Whereas if the variation quantity APLS is smaller than a limit value APLSMIN ( < O) (the absolute value is large) predetermined on the valve closing side, the variation quantity APLS is limited to the limit value APLS"IN, i.e., APLS = APLSMIN. Note that if the calculated variation quantity APLS is equal to the two limit values APLS and APLSMlN or between these two limit values, no limit is given to the variation quantity APLS. Executed subsequently in next step 206 is a process of setting a target opening obtained by adding the present opening to the variation quantity APLS of the valve opening. Subsequently, a pulse output process for setting the target opening is executed in step 207.If the present opening is over the limit opening in step 204, the operation moves to a process in step 205, wherein the target opening is calculated directly from the variation quantity APLS of the calculated valve opening. In this case, it is considered to be effective that the absolute value of the lower limit value APLS"IN on the closing side is set smaller than the absolute value of the limit value APLSSU on the opening side.

Generally, the control of the variation quantity APES1 of the valve opening under the super heat control is executed at an interval of, e.g., one minute, and the variation quantity APLS2 of the valve opening under the interrupt control is controlled depending on the change in the compressor frequency or done in the over-throttle state. Accordingly, the addition of APES1 and APLS2 is executed only when the processes of steps 201 and 203 are executed substantially simultaneously, and the limit process in step 205 is performed for each of the variation quantities APLS1 and APLS2 for the valve opening.

Hence, according to the processing shown in FIG. 4, when the valve opening is under the predetermined opening, the variation quantity of the valve opening controlled at the predetermined time interval can be restrained under the predetermined limit value. It is therefore possible to stably control the motor-operated expansion valve without causing any inconvenience due to the over-throttle state in a possible-of-compete-closing area.

As discussed above, it is effective in terms of restraining the hunting operation of the control to provide the limits respectively on the valve opening side and on the valve closing side. If the attention is paid to only such a point that the valve is completely closed during the coolant small flow rate control, however, it may follow that the limit is given to not the valve opening side but only the valve closing side. FIG. 5 is a flowchart showing specific processing procedures of the outdoor microcomputer 21 for restricting the variation quantity of the valve opening in only the closing direction, i.e., restricting a decrement quantity. Herein, after absolutely the same processes as those in steps 201 to 204 in FIG. 4 have been executed in steps 211 through 214, a magnitude of only the variation quantity APLS of the valve opening in the closing direction is restricted in step 215.That is, when the absolute value of the variation quantity APLS is larger than the absolute value of the limit value APLSMN on the closing side, the variation quantity is limited such as APLS = APLSMIN. Hereinafter, in steps 216 and 217, absolutely the same processes as -steps 206 and 207 in FIG. 4 are executed.

Thus, according to the processing shown in FIG. 5, the control of restraining the variation quantity under the predetermined control value is performed only when the valve opening is changed in only the closing direction.

With this operation also, the inconvenience due to the over-throttle state is obviated in the possible-of-complete-closing area, and the motor-operated expansion valve can be stably controlled.

As described above, the calculation of the variation quantity APES1 of the valve opening is executed at an interval of, e.g., one minute, and the variation quantity APLS2 of the valve opening under the interrupt control is calculated depending on the change in the compressor frequency or done in the over-throttle state. If assumed so, the same result is to be obtained even by giving a limit to each of the variation quantities APES1 and APLS2 of the valve opening instead of limiting the variation quantity with the addition of APES1 and APLS2.

FIG. 6 is a flowchart showing the specific processing procedures of the outdoor microcomputer 21 for executing the above control operations.

The variation quantity APES1 under the super heat control is calculated in first step 221. Subsequently, the present opening is compared with a limit opening in step 222. If the present opening is under the limit opening, the operation proceeds to a process in step 223, wherein a magnitude of the variation quantity APES1 is limited.

That is, if the variation quantity APLS1 is larger than the limit value APLSMu predetermined on the valve opening side, the variation quantity is limited such as APLS1 = APLS.

Whereas if the absolute value of the variation quantity APLS1 exceeds the absolute value of the limit value APLSMIN predetermined on the valve closing side, the variation quantity is limited such as APES1 = APLSMIN. Then, the variation quantity APLS2 for changing the compressor frequency and/or preventing the over-throttle state is calculated by the interrupt process in step 224. Then, the present opening is again compared with the limit opening in step 225. As a result of this comparison, if the present opening is smaller than the limit opening, the variation quantity APES2 is limited to the limit value APLSMIN predetermined on the valve closing side in step 226.

The variation quantity APLS of the valve opening is calculated by adding the above quantities in step 227.

Executed subsequently in next step 228 is a process of setting a target opening obtained by adding the present opening to the variation quantity APLS of the valve opening. Subsequently, a pulse output process for setting the target opening is executed in step 229. Note that when determining that the present opening exceeds the limit opening in step 225, the operation proceeds to a process in step 227 without giving any limit to the calculated variation quantity APLS2.

Thus, with also the processing shown in FIG. 6, the inconvenience due to the over-throttle state is obviated in the possible-of-complete-closing area, and the motoroperated expansion valve can be stably controlled.

On the other hand, in the air conditioner for dehumidifying by employing a part of the indoor heat exchanger as an evaporator, a temperature difference between the auxiliary heat exchanger used as an evaporator and the main heat exchanger is super-heat-controlled as a super heat quantity. In this case, the motor-operated expansion valve is greatly throttled, and hence the valve is in such a condition that the valve is easy to completely close under the super heat control. Then, as far as a dehumidifying operation is performed, the following control is effective, wherein a limit is given to the valve opening variation quantity APES1, and no limit is given to the valve opening variation quantity APES1 during a cooling operation and a heating operation.

FIG. 7 is a flowchart showing the specific processing procedures of the outdoor microcomputer 21 in the case of dehumidifying by using a part of the indoor heat exchanger as an evaporator.

Herein, the variation quantity APLS1 under the super heat control is calculated in first step 231, and, subsequently in step 232, whether a present operation mode is a dehumidifying mode or not is checked. Then, only when the operation mode is the dehumidifying mode, the present opening is compared with the limit opening in order to limit a magnitude of the variation quantity APLS1 under the super heat control. If the present opening is under the limit opening, the magnitude of the variation quantity APES1 is limited in step 234, and the operation proceeds to step 235. Absolutely the same processes as steps 224 229 shown in FIG. 6 are executed in steps 235 - 240.

Thus, even in the air conditioner for performing the humidifying process by using a part of the indoor heat exchanger as an evaporator, the inconvenience due to the over-throttle state is obviated in the possible-of-complete-closing, and the motor-operated expansion valve can be stably controlled.

By the way, the motor-operated expansion valve has a scatter in terms of the valve opening point, it is required that the limit opening for setting the area for limiting the variation quantity of the valve opening be based on the motor-operated expansion valve having a larger valve opening point. If the motor-operated expansion valve having a small valve opening point is used for the thus set limit opening, a time of reaching an optimum opening elongates, and a restoring time of a liquid back also elongates. Under such circumstances, no limit is given to the decrement quantity of the valve opening till the present opening exceeds the optimum opening, and thereafter only the decrement quantity of the valve opening is limited after changing the valve opening in the opening direction.

Thereafter,- the time of reaching the optimum opening can be decreased by giving the limit also to an increment quantity of the valve opening when changed from the opening side to the closing side.

FIG. 8 is a flowchart showing the specific processing procedures of the outdoor microcomputer 21 for controlling the motor-operated expansion valve when using the motoroperated expansion valve having the small valve opening point. In this case, it is assumed that a flag F1 be set on such a condition that the variation quantity of the valve opening changes from the closing side to the opening side after having decreased under the valve limit opening, and that a flag F2 be set on such a condition that the variation quantity of the valve opening changes reversely from the opening side to the closing side. In the following discussion, the flags are simply termed "FLG", and setting ON the flag is referred to as "FLG-ON, while setting OFF the flag is referred to as "FLG-OFF".

To start with, FLG1 and FLG2 are set OFF in step 241 when starting the operation, and subsequently in step 242 the variation quantity APES1 of the valve opening under the super heat control is calculated. Next, in step 243, whether or not the present opening is under the limit opening is checked. Then, if under the limit opening, whether FLG1 is ON or not is checked in step 244. Only when set ON, and if the absolute value of the variation quantity APES1 of the valve opening exceeds the absolute value of the limit value APLSMN determined on the valve closing side in sep 245, there is executed a process of limiting the variation quantity such as APES1 = APLSMIN.

Subsequently, whether FLG2 is ON or not is checked in step 246. Only when set ON, and if the variation quantity APLSl of the valve opening exceeds the limit value APLS 'ilY determined on the valve opening side in sep 247, there is executed a process of limiting the variation quantity such as APES1 = APLS > .

Next, in step 248, if the variation quantity APLS1 of the valve opening is determined to be in the valve opening direction, and if FLG1 is OFF, FLG1 is set ON n step 249.

Further, in step 250, if the variation quantity APES1 of the valve opening is determined to be in the valve closing direction, and if FLG1 is ON, FLG2 is set ON in step 249.

Calculated thereafter in step 252 is the variation quantity APLS2 for changing the compressor frequency and/or preventing the over-throttle state by the interrupt process, and, in next step 254, the limit opening is compared with the present opening. Then, as far as the present opening is under the limit opening, there is executed a process of the restraint to the limit value APLSMIN of the variation quantity #PLS2 of the valve opening. In step 255, the variation quantity APLS is calculated by adding the variation quantities APLS1 and APLS2 of the valve opening. Executed then in next step 256 is a process of setting a target opening obtained by adding the present opening to the variation quantity APLS of the valve opening. Subsequently, a pulse output process for attaining the target opening is executed in step 257.

Next, whether or nor the present opening is under the limit opening is checked in step 258. If the present opening exceeds the limit opening, the operation returns to the process in step 241. If the present opening is throttled down under the limit opening, the operation returns to the process in step 242. Note that when determining that the present opening exceeds the limit opening in step 243, no limit is given to the calculated variation quantities APES1 and APLS2, and besides, the operation proceeds to step 252 and subsequent steps without setting ON/OFF FLG.

When comparing a case where the processes shown in FIG.

8 are executed with a case of simply making the limit only in the valve closing direction, a difference is as shown in FIGS. 10A and lOB. Now, supposing that the limit value APLS MAX in the closing direction is set relatively small by using the motor-operated expansion valve with a small valve opening point, as shown in FIG. lOB, the valve opening decreases uniformly stepwise under the limit opening, and therefore a time of reaching the optimum opening elongates.

On the other hand, when executing the processes shown in FIG. 8, as shown in FIG. 10A, since no limit is given at first to even the limit area of the variation quantity of the valve opening, although slightly excessively throttled for the optimum opening, the valve opening changes from the closing direction to the opening direction at that point of time. Hence, the valve opening is directly changed in the opening direction without any limit, and a limit is given to the variation quantity in the closing direction from that stage. Besides, the limit is given to the variation quantity in the opening direction just when the valve opening changes from the opening direction to the closing direction, and hence the time of reaching the optimum control quantity obviously becomes shorter than shown in FIG. lOB.

Thus, with the execution of the processes shown in FIG.

8, the inconvenience due to the over-throttle state is obviated in the possible-of-complete-closing area, and the motor-operated expansion valve can be stably controlled.

Besides, it is feasible to reduce the time of reaching the optimum opening by using even the motor-operated expansion valve having the small valve opening point.

As discussed above, the limit value for the variation quantity of the valve opening can be determined in relation to the limit opening. However, the hunting phenomenon is easy to occur if set large in order to shorten the time of reaching the optimum control. If the decrement quantity of the valve opening is set to the limit opening or under, the target opening is set to the limit opening just when the valve opening is decreases under the limit opening.

With this setting, the valve opening can be approximated to a critical point with respect to the optimum opening.

FIG. 9 is a flowchart showing the specific processing procedures of the outdoor microcomputer 21 for performing the control described above. Herein, the same processes as those shown in FIG. 6 are executed in steps 261 - 268, and subsequently whether or not the target opening is under the limit opening is checked in step 269. If the target opening is the limit opening, the target opening is determined to be the limit opening in step 270, and thereafter the pulse output process for setting the target opening is executed in step 270.

Thus, with the execution of the precesses shown in FIG.

It is apparent that, in this invention, a wide range of different working modes can be formed based on the invention without deviating from the spirit and scope of the invention. This invention is not restricted by its specific working modes except being limited by the appended claims.

Claims

CLAIMS:

1. An air conditioner, having a refrigerating cycle including a closable motor-operated expansion valve, for controlling an opening of said motor-operated expansion valve at an interval of a predetermined time, said air conditioner characterised by: control means for limiting a variation quantity of the valve opening to a predetermined value or under when a valve opening is under a predetermined opening.

2. An air conditioner according to claim 1, wherein said control means limits the variation of the valve opening to the predetermined value or under only when changing the valve opening in only a closing direction.

3. An air conditioner having a refrigerating cycle including a closable motor-operated expansion valve and a capability variable compressor, said air conditioner characterised by: control. means for limiting a variation quantity of a valve opening to a predetermined value or under when the valve opening is under a predetermined opening on the occasion of super-heat-controlling the valve opening of said motor-operated expansion valve at an interval of a predetermined time, and for limiting the variation quantity of the valve opening to the predetermined value or under only when the valve opening is under the predetermined opening and when the valve opening is changed in a closing direction on the occasion of controlling the valve opening of said motor-operated expansion valve on the basis of a change in capability of said compressor.

4. An air conditioner having a refrigerating cycle including a closable motor-operated expansion valve and a capability variable compressor, said air conditioner characterised by: valve opening limiting means for limiting a decremen.

quantity of a valve opening to a predetermined value or under when the valve opening of said motor-operated expansion valve is controlled in a closing direction after controlling at first the valve opening in an opening direction since the valve opening decreased under a predetermined opening on the occasion of super-heatcontrolling the valve opening of said motor-operated expansion valve at an interval of a predetermined time.

5. An air conditioner according to claim 4, characterised by: second valve opening limiting means for limiting the increment quantity of the valve opening when controlling at first the valve opening in the opening direction since the valve opening decreased under the predetermined opening, thereafter controlling the valve opening of said motor-operated expansion valve in the closing direction, and thereafter controlling once again the valve opening of said motor-operated expansion valve in the opening direction on the occasion of super-heat-controlling the valve opening of said motor-operated expansion valve at the interval of the predetermined time.

6. An air conditioner according to any one of claims 1 to 5, characterised by: valve opening holding means for temporarily holding the valve opening of siad motor-operated expansion valve to a predetermined opening when the valve opening is reduced under the predetermined opening from a position with a valve opening larger than the predetermined opening.

7. An air conditioner according to any one of claims 1 to 6, characterised by: initial opening control means for fixing the opening of said motor-operated expansion valve to an opening larger than the predetermined opening when starting an operation of said air conditioner.

8. An air conditioner substantially as hereinbefore described with reference to any of the accompanying drawings.