Method of controlling compressor and controller

A compressor is operable to compress refrigerant at a variable operation frequency. According to a method of controlling the compressor, the compressor starts operating, and just after that, the compressor operates at a first frequency for a first period of time. Just after that, the compressor operates at a second frequency lower than the first frequency for a second period of time longer than the first period, and after that, the compressor operates at an ordinary operation. This method does not cause the compressor to generate an abnormal noise or obstruction to lubrication.

TECHNICAL FIELD

The present invention relates to a method of controlling a refrigerant compressor used in refrigerating devices, such as a refrigerator, an air-conditioner, and a refrigerator with a freezer, and to a controller for controlling the compressor.

BACKGROUND ART

Compressors of refrigerating devices, such as a domestic refrigerator with a freezer, recently employ hydrocarbon refrigerant, such as R600a, which is a natural refrigerant having an ozone depleting coefficient of zero and a small global warming coefficient.

A conventional compressor disclosed in Japanese Patent Laid-Open Publication No. 11-311457 rotates at a low frequency at its start at a low ambient temperature, at which a large amount of refrigerant dissolves in lubricant. At the start, the lubricant is discharged while bubbles generated by vaporization of the refrigerant are sucked. When the compressor rotates at a constant frequency, a discharged amount of the lubricant decreases. As a result, an amount of the lubricant in the compressor is maintained, and this prevents lack of the lubricant supplied to sliding components.

A controller of controlling the conventional compressor will be described hereinafter.FIG. 10is a sectional view of a conventional refrigerator.FIG. 11shows a refrigerating cycle of the conventional refrigerator.FIG. 12is an electrical schematic diagram of the conventional refrigerator.FIG. 13shows a change of an operating frequency of the conventional compressor.

As shown inFIG. 10, reciprocating compressor10is placed at the lower and rear section in refrigerator1. The reciprocating compressor includes lubricant, motor11, and a mechanism driven by motor11. Those elements are accommodated in an airtight container. Compressor10includes a lubricating mechanism (not shown) formed of a centrifugal pump therein. The airtight container accommodates compressor motor11, a crank mechanism (not shown), and a piston (not shown). A rotary shaft of motor11is linked to the piston via the crank mechanism which converts a torque of motor11into a linear reciprocating force and transmits the force to the piston. Refrigerant in the airtight container is compressed by the reciprocating force of the piston.

As shown inFIG. 11, compressor10is coupled to condenser13via pipe12a. Condenser13is coupled to capillary tube14via pipe12b. Capillary tube14is coupled to evaporator15via pipe12c. Evaporator15is coupled to a suction inlet of compressor10via pipe12d. The foregoing structure forms refrigerating cycle16having refrigerant sealed therein.

As shown inFIG. 12, motor11is a three-phase DC brush-less motor including a stator formed of a stator core having coils11aof phases U, V and W wound around the core, and a rotor formed of a rotor core and permanent magnets rigidly mounted to the rotor core. Motor11is coupled to inverter18shown inFIG. 12.

Inverter18includes main controller22implemented mainly by a micro-computer. Main controller22determines an operating frequency of motor11in response to an electrical signal corresponding to room temperature T. The electrical signal is supplied from room-temperature sensor28, such as a thermister, placed at refrigerator1.

An operation of the controller of the refrigerant compressor will be described hereinafter. Upon inverter18outputting a power at a predetermined frequency to motor11, compressor10compresses the refrigerant, then the refrigerant discharged from compressor10circulates through condenser13, capillary tube14, and evaporator15in this order.

A large amount of refrigerant generally dissolves into lubricant in compressor10at a low ambient temperature. At this moment, if compressor10is activated at a high frequency, the dissolving refrigerant evaporates at once, thereby producing bubbles intensely.

In order to prevent the bubbles from being produced, when main controller22of inverter18detects the relation of reference temperature T0≧ambient temperature T, the controller raises the frequency of the power applied to motor11from 0 Hz (the motor halts) to 30 Hz, which is a minimum frequency, within about 3 seconds, then holds the frequency at 30 Hz. This operation allows the refrigerant dissolving in the lubricant to evaporate gradually, hence preventing the bubbles from being intensely produced. Then, the lubricant is prevented from being discharged from compressor10together with the refrigerant, and the lack of lubrication can be prevented.

However, when compressor10operates at the minimum frequency (30 Hz) at a low ambient temperature, in the conventional controller, the refrigerant dissolving in the lubricant evaporate little. Therefore, at low ambient temperature at which the large amount of the refrigerant dissolves in the lubricant, when the compressor operates from the frequency of 30 Hz to an ordinary operation at a high rotation speed, a large amount of the refrigerant evaporates at once, hence producing the bubbles intensely. Compressor10then compresses the refrigerant together with the bubbles including a large amount of lubricant, thereby generating an abnormal noise. Simultaneously to this, an amount of lubricant is discharged from compressor10, and then, a lack of lubrication and an obstacle to lubrication occur in compressor10.

It has taken a long period of time for the refrigerant to dissolve in the lubricant. Therefore, the above phenomenon often occurs at an initial starting, i.e., when a refrigerating device is energized for the first time. This phenomenon often occurs at a start after a defrosting operation since the refrigerant in condensed form returns into compressor10from evaporator15.

For a combination of hydrocarbon refrigerant, such as R600a, recently introduced and lubricant made from mineral oil, a saturation solubility of the refrigerant to the lubricant depends extremely on a pressure. At the start of the compressor, the pressure in the airtight container is reduced, hence producing the bubble intensely.

SUMMARY OF THE INVENTION

A compressor is operable to compress refrigerant at a variable operation frequency. According to a method of controlling the compressor, the compressor starts operating, and just after that, the compressor operates at a first frequency for a first period of time. Just after that, the compressor operates at a second frequency lower than the first frequency for a second period of time longer than the first period of time, and after that, the compressor operates at an ordinary operation.

This method does not cause the compressor to generate an abnormal noise or obstruction to lubrication.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a vertical sectional view of a refrigerant compressor in accordance with Exemplary Embodiments 1 to 3 of the present invention. Refrigerant compressor99which can operate at a variable operation frequency contains hydrocarbon refrigerant, such as R600a, which does not include chlorine or fluorine. Airtight container101accommodates motor element104formed of stator102and rotor103, and compressor element105driven by motor element104.

Airtight container101stores lubricant106made from mineral oil which is highly soluble with the refrigerant. Crankshaft107includes a lubricating mechanism (not shown) therein. Crankshaft107includes main shaft108having rotor103press-fixed thereto and eccentric section109formed eccentrically with respect to main shaft108. Crankshaft107is supported by cylinder block110.

A suction pipe (not shown) is fixed to airtight container101and coupled to a lower pressure side (not shown) of a refrigerating system, thereby guiding the refrigerant into container101. Suction muffler116has an end communicating with compressing chamber111via suction port117. Suction inlet118opens in container101and fixed by being sandwiched between bulb-plate119and cylinder heat120.

FIG. 2shows a top view of rotor103of compressor99, andFIG. 3shows a top view of stator102of compressor99. Rotor103includes rotor core121, cylindrical pipes122, and permanent magnets123embedded between core121and pipes122. A lid (not shown) is fixed to core121with rivets124. Coil wires127are wound directly on teeth126of core125, thereby providing stator102. Lubricant106lubricates the foregoing elements of the compressor.

Controller128controls an operation frequency of the compressor, as shown inFIG. 5before an ordinary operation in which the compressor for compressing the refrigerant in the refrigerating device operates ordinarily, for example, when the refrigerating device is connected to a commercial power supply or when the refrigerating device is turned on for the first time after a defrosting operation. Compressor99is driven at a high speed at a frequency over 40 Hz at first within two seconds (high-speed operation132). Then, the compressor is driven at a lower speed at a frequency not higher than 35 Hz (low-speed operation133). A cycle consisting of the high-speed operation and the low-speed operation is repeated again, then controller128has compressor99operate at a rated operation frequency (rated operation137, i.e., ordinary operation137). At the start of the compressor, the refrigerating device is connected to the commercial power supply. Even if a large amount of the refrigerant dissolves into the lubricant in the compressor, the high-speed operation allows the refrigerant dissolving in the lubricant to evaporate, thereby preventing suction of bubbles. At another start of the compressor, i.e. the compressor is turned on for the first time after a defrosting operation, a large amount of liquid refrigerant returns from the refrigerating device to the compressor. Even if a large amount of the refrigerant dissolves in the lubricant, the high-speed operation allows the refrigerant dissolving in the lubricant to evaporate, thereby preventing the compressing chamber from having the bubbles sucked into it.

Motor element104, upon receiving a current, activates compressor99. Rotor103rotates crankshaft107, and motion of eccentric section109is transmitted to piston113via linking unit114, thereby having piston113reciprocate in compressing chamber111. The refrigerant guided into airtight container101through the suction pipe is sucked with suction muffler116. Then, a suction reed (not shown) opens to allow the refrigerant to flow through suction port117. Then, the refrigerant is guided into compressing chamber111and is compressed continuously.

Just after compressor99starts operating at the frequency over 40 Hz (high-speed operation132), a pressure in airtight container101is reduced. Further, lubricant106is agitated, which allows the refrigerant dissolving in lubricant106to evaporate, and bubbles134are produced, as shown inFIG. 6.

The refrigerant is hydrocarbon refrigerant excluding chlorine and fluorine, and lubricant106is made from mineral oil which is mutually soluble with the refrigerant. For a combination of this refrigerant and this lubricant, a saturation soluble amount of the refrigerant into lubricant106decreases rapidly according to decreasing of the pressure, so that the refrigerant evaporates intensely at once to produce the bubbles.

Since high-speed operation132is performed for a period of time limited within 2 seconds, controller128then drives compressor99at a frequency not higher than 35 Hz (change to low-speed operation133) before bubbles134reach suction inlet118of suction muffler116. The period of time of 2 seconds is the maximum allowable period of time before bubbles134reach suction inlet118at the fastest rising speed in the case of producing the most intense bubbles.

In other words, before bubbles134is sucked by suction muffler116, controller128changes the operation of compressor99to low-speed operation133at a frequency not higher than 35 Hz. At low-speed operation133, the pressure is reduced moderately, and lubricant106is not agitated so much, hence having bubbles134fall but not rise.

The cycle consisting of high-speed operation132and low-speed operation133is repeated before the ordinary operation, so that the refrigerant dissolving in lubricant106evaporates before bubbles134are sucked into compressing chamber111, and the bubble phenomenon is suppressed to a small scale. Then, bubbles134fall, and then, compressor99is switched to operate at low-speed operation133.

The refrigerant in lubricant106produces the bubbles and evaporates at high-speed operation132, hence preventing an abnormal noise due to the compression of the lubricant. As a result, lubricant106is discharged little, so that an obstruction to lubrication caused by the lower oil surface can be prevented.

At low-speed operation133, compressor99may stop, i.e. at an operating frequency of 0 Hz, hence minimizing the bubbles.

Suction inlet118provided at suction muffler116and opening into airtight container101allows bubbles134not to be guided directly to compressing chamber111, but to be guided to chamber111through suction inlet118and suction muffler116. Therefore, even if bubbles134are sucked into inlet118, isolation of the lubricant and heat exchange in muffler116facilitates the evaporation of the refrigerant, hence suppressing the suction of foams134into chamber111.

Motor element104includes rotor103having permanent magnets123, and stator102having coil wires127wound directly on teeth126of stator core125. Motor element104allows core125to be thin, and allows airtight container101to be small. As a result, the amount of lubricant106stored in container101is smaller by 25% than that in a motor element using a distributed winding. This reduction allows an amount of refrigerant dissolving in lubricant106to be smaller proportionately, thereby suppressing the bubbles.

FIG. 7shows operating frequencies at the start of a refrigerant compressor in accordance with Exemplary Embodiment 2 of the present invention. Similar elements to those of Embodiment 1 are denoted by the same reference numerals as those of Embodiment 1, and their detailed descriptions thereof are omitted here. As shown inFIG. 7, controller128drives refrigerant compressor99at frequency Fa (high-speed operation132) before an ordinary operation in which the compressor for compressing refrigerant in a refrigerating device operates ordinarily, for example, when the refrigerating device is connected to a commercial power supply or when the device is turned on for the first time after a defrosting operation. Then controller128drives compressor99to operate at frequency Fb (low-speed operation133) lower than frequency Fa. A cycle consisting of high-speed operation132and low-speed operation133is repeated plural times.

Then, controller128drives compressor99to operate at frequency Fb (low-speed operation133b) for period T2of time shorter than period T1, so that the production of bubbles134is suppressed. The amount of bubbles134at low-speed operation133bis less than the amount of bubbles134at low-speed operation133a, hence allowing period T2to be shorter than period Ti to suppress the production of bubbles134.

Then, controller128drives compressor99to operate at frequency Fa (high-speed operation132c), thereby allowing the refrigerant still remaining in lubricant106to evaporate completely. Then, controller128drives compressor99to operate at frequency Fb (low-speed operation133c) for period T3of time shorter than period T1and period T2. Since high-speed operation132cproduces a fewer amount of bubbles134, low-speed operation133cfor period T3shorter than period T1and period T2is enough to suppress the production of bubbles134.

If periods T1-T3are shortened step by step, respective periods of low-speed operations133a-133ccan be shortened. As a result, the proportions of high-speed operations132a-132cbecomes greater, hence allowing the lubricant to be supplied to sliding components.

Compressor99operates at frequency Fa throughout high-speed operations132a-132c. However, as long as frequency Fa is higher than frequency Fb at low-speed operations133a-133c, and as long as operation periods of the high-speed operations are longer than periods T1-T3of low-speed operations, effects similar to above are expected. At low-speed operations133a-133c, the compressor may not be driven necessarily at common frequency Fb, but may be driven at respective frequencies at low-speed operations133a-133cdifferent from each other as long as the frequencies are lower than respective frequencies at high-speed operations132a-132c.

FIG. 8shows operating frequencies used at the start of a refrigerant compressor in accordance with Exemplary Embodiment 3 of the present invention. Similar elements to those of Embodiment 1 are denoted by the same reference numerals as those of Embodiment 1, and detailed descriptions thereof are omitted.

As shown inFIG. 8, controller128drives refrigerant compressor99to operate at frequencies F1-F4before an ordinary operation in which the compressor for compressing refrigerant in a refrigerating device operates ordinarily, for example, when the refrigerating device is connected to a commercial power supply or when the device is turned on for the first time after a defrosting operation. First, controller128drives compressor99to operate at frequency F1(high-speed operation135a), and then drive the compressor to operate at frequency F4(low-speed operation136a) lower than frequency F1. During high-speed operation135a, bubbles134are produced. However the production of bubbles134is suppressed during low-speed operation136a.

Then, controller128drives compressor99to operate at frequency F2(high-speed operation135b) higher than frequency F1, so that refrigerant still dissolving in lubricant106evaporates due to agitation and lowering of pressure. Then, controller128drives compressor99to operate at frequency F4(low-speed operation136b). The amount of bubbles134produced during low-speed operation136bis smaller than that during high-speed operation135a, so that the production of bubbles134can be sufficiently suppressed during low-speed operation136b.

Next, controller128drives compressor99to operate at frequency F3(high-speed operation135c) higher than frequency F2, thereby allowing the refrigerant to still dissolve in lubricant106to evaporate completely. Then, controller128drives compressor99to operate at frequency F4(low-speed operation136c). The amount of bubbles134produced during high-speed operation135cis smaller than that produced during high-speed operation135b, so that the production of bubbles134can be sufficiently suppressed during low-speed operation136c. Since an average frequency at high-speed operations135a-135cbecomes higher, the lubricant is supplied stably to sliding components.

FIG. 9Ais a sectional view of a refrigerating device including a refrigerant compressor and a controller in accordance with Exemplary Embodiment 4 of the present invention. Similar elements to those of Embodiment 1 are denoted by the same reference numerals as those of Embodiment 1, and detailed descriptions thereof are omitted. Refrigerating device139includes storage compartment141surrounded by heat insulator140, refrigerant compressor99placed at the bottom of the device, a condenser, a decompressor, and evaporator144.

FIG. 9Bshows a refrigerating cycle of the refrigerating device of Embodiment 4. Compressor99, condenser150, decompressor151, and evaporator144are coupled to provide the refrigerating cycle. As shown inFIG. 1, compressor99includes lubricant106, motor element104including stator102and rotor103, and compressor element105in airtight container101. Motor element104is controlled and driven by controller128according to Embodiment 1 shown inFIG. 1.

Compressor99prevents compressing chamber111from sucking bubbles134into the chamber, and allows refrigerant dissolving in lubricant106to evaporate sufficiently, thereby supplying the lubricant adequately to sliding components.

At each of high-speed operations135a-135c, the compressor may operate for different periods of time. At each of low-speed operations136a-136c, the compressor may operate not necessarily at common frequency F4. As long as respective frequencies of the low-speed operations are lower than frequencies F1-F3of high-speed operations135a-135c, the frequencies of the low-speed operation may be different from each other.

According to Embodiments 1 to 4, compressor99is the reciprocating compressor including the airtight container have a low pressure therein is described. However, compressor99may be a compressor other than the reciprocating compressor, i.e., a compressor including an airtight container having a high pressure therein, and the methods according to Embodiment 1 to 3 suppress bubbles produced in lubricant.

INDUSTRIAL APPLICABILITY

A method of controlling a compressor for compressing refrigerant at a variable operation frequency according to the present invention prevents an abnormal noise and an obstruction to lubrication.

REFERENCE NUMERALS