Gas compressor with oil separator

Abstract: A gas compressor is provided which is suitable to enhance a refrigeration efficiency of an air conditioning system (8) and to avoid lubrication fault due to oil shortage. A volume of a discharge chamber (7) is enlarged, and an easy-to-be soluble combination of refrigerant gas and oil is selected. When the volume of the discharge chamber is enlarged, high-pressure refrigerant gas including non-separated oil component takes a sufficient time to pass through the discharge chamber. If the passage time for the discharge chamber is thus elongated, a ratio of the non-separated oil component contained in the high-pressure refrigerant gas to drop down to an oil pool (7b) at a bottom of the discharge chamber by a gravatational force is high so that an entrance amount of the non-separated oil component toward a condenser of the air conditioning system may be reduced as much as possible and the oil within the gas compressor is likely to return to reserve a sufficient amount of the oil in the gas compressor.

Description: The present invention relates to a gas compressor used in an air conditioning system and more particularly to a gas compressor that may enhance the refrigeration efficiency in the air conditioning system and may prevent the lubrication fault caused by oil shortage. As shown in Fig. 8, conventionally, in such a kind of the gas compressor, a compressor body 4, an oil separator 5 and the like are received in a casing 3 composed of a case 1 opened at one end and a front head 2 mounted on the open end. A space formed between the inside of the casing 3 and the front portion of the compressor body 4 is formed as a suction chamber 6, and a space formed between the inside of the casing 3 and the rear portion of the compressor body 4 is formed as a discharge chamber 7. When a rotor 4b is rotated together with a rotor shaft 4a, the compressor body 4 sucks low pressure refrigerant gas from the suction chamber 6 into a cylinder 4d through a front side block 4c, compresses the low pressure refrigerant gas together with lubricant oil and discharges from a rear side block 4e toward the discharge chamber 7. Also, the oil separator 5 is mounted on the rear side block 4e of the compressor body 4 for separating high-pressure refrigerant gas, discharged from the compressor body 4 toward the discharge chamber 7, into a gas component and an oil component. The thus separated gas component passes from the discharge chamber 7 through a discharge port 7a of the case 1, a condenser 9 of an air conditioning system 8 shown in Fig. 9, an expansion valve 10, an evaporator 11 and the like and thereafter is returned to the suction chamber 6 from a suction port 6a to be again compressed together with the oil as the refrigerant gas. On the other hand, the oil component is temporarily reserved in an oil pool 7b at the bottom portion of the discharge chamber 7 and is again compressed together with the refrigerant gas. However, in such a conventional gas compressor, although the high-pressure refrigerant gas discharged from the compressor body 4 is fed into the oil separator 5, it is difficult to completely separate the high-pressure refrigerant gas into the gas component and the oil component by the oil separator. As a result, the oil component that could not be completely separated (hereinafter also referred to as "non-separated oil component") is caused to flow as a mist oil to the condenser 9 of the air conditioning system 8, the evaporator 11 and the like so that the oil circulation ratio (hereinafter also referred to as OCR) of the air conditioning system 8 is high and a large amount of the oil that inherently has nothing to do with the refrigeration is recirculated within the air conditioning system 8 to degrade the refrigeration efficiency. Also, when the oil component is caused to flow toward the condenser 9 of the air conditioning system 8, the amount of oil within the gas compressor is reduced to cause such a problem that the lubrication fault of the gas compressor due to the oil shortage would occur. Furthermore, in order to separate the gas component and the oil component of the refrigerant gas at a higher ratio, it is possible to consider using the combination in which the refrigerant gas and the oil are hardly mixed with each other. However, the oil that has been discharged from the gas compressor is cooled within the evaporator 11 and the like and the viscosity of the oil is increased so that the oil will not return to the gas compressor. Thus, there is a problem that the lubrication fault of the gas compressor due to the oil shortage would occur. US 4478054 describes a helical screw compressor in which the oil and a condensed refrigerant are directed to an oil sump which is 1.5 times the volume of the oil required to lubricate the compressor. EP 0538973A describes an air compressor including a housing having a hood part which accommodates a filter element which is used to minimise the oil in the compressed air reaching a compressed air outlet. US 5733107 discloses a lubrication oil separation mechanism for a compressor in which refrigerant gas, including misted lubrication oil, is caused to circulate around an oil separation cylinder. The misted oil separates from the refrigerant gas through centrifugal action and falls back under gravity to the bottom of a compressor discharge chamber. EP 0201672A describes a screw-type compressor having a compressor unit mounted in a vertically disposed housing. The housing top plate supports two oil separators to separate out any oil in the compressor air outlet supply for return to an oil sump. JP 59099079A discloses a gas/liquid separation device for a refrigeration compressor. The device includes a separation chamber having an entry port which communicates with the delivery port of the main compressor. The separation chamber has a planar plate and oil mist in the discharged compressed gas adheres to the plate and then fall back to an oil reservoir under gravity. US 5211031 describes a compressor having a pair of scroll-type compression units arranged in a hermetic casing. Oil which is discharged with the compressed gas through a discharge port is separated within the casing and returned to an oil reservoir. JP 04109090A describes a closed type compressor having two compressor main bodies accommodated side by side in a single casing. US 5542266 describes a refrigeration compressor including an oil separation passage auxiliary to a main discharge chamber. Compressed refrigerant gas containing lubrication oil is passed through the separation passage to separate the lubrication oil, from where it is then returned to an oil sump. EP 0738539A discloses a refrigeration compressor in which a lubrication oil is selected to be insoluble in and has a lower specific gravity than the refrigerant. Oil/refrigerant mixture is passed through an accumulator having an oil return hole formed in a side wall of a suction pipe. The oil, being insoluble in the refrigerant, is detained on the surface of the refrigerant and is thus separated as the mixture passes through the hole, and is then returned to the sump. In order to overcome the above-noted defects inherent in the prior art, an object of the present invention is to provide a gas compressor that is suitable for enhancement of the refrigeration efficiency of an air conditioning system and to prevent the lubrication fault due to the oil shortage. In order to attain the above-mentioned objects, according to the invention, there is provided a gas compressor comprising: a compressor body for sucking refrigerant gas and compressing the refrigerant gas together with oil for lubrication and for discharging the compressed refrigerant gas and oil; and an oil separator for separating refrigerant gas after compression and discharged from said compressor body into a gas component and an oil component, characterised by further comprising: a one-piece or monolithic case receiving therein said compressor body and said oil separator, the case having a barrel portion having a first diameter, surrounding and contacting hermetically with a peripheral surface of said compressor body and facing and contacting hermetically with an end surface of a front head which covers an end of the compressor body, and an enlarged case portion having a second diameter greater than the first diameter and extending from the barrel portion, the enlarged case portion having a discharge chamber for temporarily holding the gas component and the oil component separated by said oil separator and provided with a discharge port for discharging the gas component to an air conditioning system and an oil pool for receiving the oil component at a bottom with a space volume dimensioned to suppress an oil circulation ratio of the air conditioning system and to keep a sufficient amount of oil within said gas compressor body. According to the present invention, there are provided a casing for receiving the compressor body and the oil separator. A space defined between the inside of the casing and the front portion of the compressor body is formed into a suction chamber, and a space defined between the inside of the casing and the rear portion of the compressor body is formed into a discharge chamber. The space volume of the above-described discharge chamber is enlarged by projecting the inside of the casing to the outside. According to the present invention, there is provided a gas compressor comprising a plurality of compressor bodies and a single discharge chamber. The gas compressor according to the invention is characterised in that the discharge chamber has a space volume that is two times to ten times larger than a sucked gas displacement per one revolution of the compressor bodies. The gas compressor according to the invention is characterised in that the single discharge chamber has a space volume that is ten times to thirty times larger than a sucked gas displacement per one revolution of a plurality of body. The gas compressor according to the invention is characterised in that the combination of the oil and the refrigerant gas is one selected from a group essentially consisting of PAG system oil and R22 refrigerant, PAG system oil and R407C refrigerant, ether system oil and R407C refrigerant, carbonate system oil and R407C refrigerant, carbonate system oil and R410a refrigerant, ester system oil and R410a refrigerant and PAG system oil and R134a refrigerant. According to the present invention, since the space volume of the discharge chamber is large as described above, the high-pressure refrigerant gas including the oil component (non-separated oil component) that could not be separated by the oil separator is stagnant in the discharge chamber for a long period of time. The ratio of the non-separated oil component to drop by its gravitational force down to the oil pool at the bottom of the discharge chamber to thereby considerably reduce the entrance amount of the non-separated oil component to the condenser, the evaporator and the like of the air conditioning system. Note that, in the present invention, the oil circulation ratio or OCR means the ratio of the oil component amount relative to the entire amount of the mixture of the refrigerant gas component and the oil component at any desired position within the air conditioning system except for the compressor when a part of the oil filled within the compressor is discharged to the air conditioning system by the operation of the compressor. Also, the sucked gas displacement volume per one revolution of the compressor means, in the structure where the refrigerant gas is compressed by the compressor body due to the rotation of the rotor, a theoretical volume of the sucked gas, to be discharged during one revolution of the rotor, which may be calculated in accordance with a dimension and a structure of the compressor body. The PAG term is an abridgement of polyalikylene glycol. Embodiments of the present invention will now be described by way of further example only and with reference to the accompanying drawings, in which:- Fig. 1 is a longitudinal sectional view showing a gas compressor in accordance with an embodiment of the present invention (single compressor); Fig. 2 is a sectional view taken along the line A of Fig. 1; Fig. 3 is a partially fragmentary view of a gas compressor in accordance with another embodiment of the present invention as viewed from above (multi-compressor); Fig. 4 is a cross-sectional view taken along the line A-A of Fig. 3; Fig. 5 is a graph showing a relationship between an OCR and a ratio of a discharge chamber space volume relative to a sucked gas displacement volume per one revolution of the single compressor shown in Fig. 1; Fig. 6 is a graph showing a relationship between an OCR and a ratio of a discharge chamber space volume relative to a sucked gas displacement volume per one revolution of the multi-compressor shown in Fig. 3; Fig. 7 is a graph showing a relationship between temperature and pressure due to differences in combination of the refrigerant gas and oil when the refrigerant gas is dissolved into the oil by 10%; Fig. 8 is a cross-sectional view showing a conventional gas compressor; and Fig. 9 is an illustration of an air conditioning system. A gas compressor in accordance with an embodiment of the present invention will now be described in detail with reference to the Figures. Incidentally, the basic structure of the gas compressor is substantially the same as that of the convention one. Namely, the gas compressor has the compressor body 4, the oil separator 5 and the like. The compressor body 4 compresses the refrigerant gas of the suction chamber 6 together with the lubrication oil and discharges this to the discharge chamber 7. Also, the oil separator 5 separates the high-pressure refrigerant gas, discharged from the compressor body 4, into the gas component and the oil component. Accordingly, the same reference numerals are used to designate the like component and the detailed explanation therefore will be omitted. In the gas compressor shown in Fig. 1, a space volume of the discharge chamber is increased in comparison with the conventional gas compressor (see Fig. 8) . The gas compressor provides a large volume discharge chamber 7. More specifically, the gas compressor shown in Fig. 1 has a casing 3 for receiving a compressor body 4 and an oil separator 5. The space defined between the inside of the casing 3 and the front portion of the compressor body 4 is formed into the suction chamber 6 and the space defined between the inside of the casing 3 and the rear portion of the compressor body 4 is formed into the discharged chamber 7 as in the conventional compressor. However, in the gas compressor shown in Fig. 1, in order to much enlarge the space volume of the discharge chamber 7 in comparison with the conventional gas compressor, an inside (an inner wall surface on the rear portion of the case body 1) forming the inner wall of the discharge chamber 7 is expanded to the outside as one means for enlarging the volume. This is different from the structure of the conventional compressor. Namely, in the gas compressor shown in Fig. 1, the rear portion of the casing 3 has an outer appearance so that the rear portion of the casing 3 is largely inflated from a barrel portion 3a (a waist portion surrounding the outer periphery of the compressor body 4) . The inside of the portion that appears to be inflated is the large volume discharge chamber 7. As the space volume of the discharge chamber 7 is enlarged, the high-pressure refrigerant gas including the non-separated oil component (oil component that could not be separated by the oil separator 5) takes a sufficient time to pass through the discharge chamber 7 and to reach the discharge port 7a. As the passage time of the high-pressure refrigerant gas through the discharge chamber is thus elongated, the amount of the non-separated oil component contained in the high refrigerant gas, to drop by its gravitational force to the oil pool 7b of the bottom portion of the discharge chamber, is increased in comparison with the conventional case. It is therefore possible to considerably decrease the entrance amount of the non-separated oil component to the condenser 9 (see Fig. 9) of the air conditioning system 8, and to reserve a sufficient amount of the oil within the gas compressor. The volume of the discharge chamber 7 is increased in comparison with the conventional case so that the volume is enlarged up to a large volume enough to keep a sufficient amount of oil and to reduce the oil circulation ratio within the air conditioning system 8. The operation of the thus constructed gas compressor will now be described with reference to Fig. 1. Incidentally, the following operation is the same as in the conventional case. Namely, when the operation of the gas compressor is started, the refrigerant gas is sucked into the compressor body 4 from the suction chamber 6, and the sucked refrigerant gas is compressed together with the oil within the compressor body 4 and thereafter discharged toward the discharge chamber 7 as the high-pressure refrigerant gas. Also, the high-pressure refrigerant gas discharged from the compressor body 4 toward the discharge chamber 7 is separated into a gas component and an oil component by the oil separator 5. The gas component passes from the discharge chamber 7 through the discharge port 7a of the case 1, the condenser 9 or the like of the air conditioning system 8 and thereafter is returned to the suction chamber 6 from the suction port 6a to be again compressed together with the oil as the refrigerant gas. On the other hand, the oil component is temporarily reserved in the oil pool 7b at the bottom portion of the discharge chamber 7 and is again compressed together with the refrigerant gas. This operation is substantially the same as that of the conventional case. Also, in this gas compressor, it is difficult to completely separate the high-pressure refrigerant gas, discharged from the compressor body 4, into the gas component and the oil component by the oil separator 5. The oil component (non-separated oil component) that has not been completely separated is contained in the state of mist oil in the high-pressure refrigerant gas of the discharge chamber 7. However, an amount of the oil, that is to flow out toward the condenser 9 (see Fig. 9) of the air conditioning system, out of such a non-separated oil component, is very small, and a large amount of the non-separated oil is to drop down toward the oil pool 7b of the bottom of the discharge chamber 7. Namely, in the gas compressor shown in Fig. 1, since the space volume of the discharge chamber 7 is increased in comparison with the conventional case, the stagnation time of the high-pressure refrigerant gas including the non-separated oil component in the discharge chamber is elongated in comparison with the conventionally structured gas compressor which is temporarily less on hold. As a result, a large amount of the non-separated oil component drops down to the oil pool 7b at the bottom of the discharge chamber 7 by the gravitational force. For this reason, the flow-out amount of the non-separated component to the condenser 9 of the air conditioning system 8 is largely reduced and the oil circulation ratio of the air conditioning system 8 is lowered. Accordingly, the large amount of the oil that inherently has nothing to do with the refrigeration is prevented from being recirculated through the air conditioning system 8 and it is therefore possible to suppress the oil circulation ratio of the air conditioning system 8 to a lower level to enhance the refrigeration efficiency. Also, a sufficient amount of oil may be reserved in the gas compressor to thereby prevent the lubrication fault of the gas compressor due to the oil shortage. Incidentally, in the foregoing embodiment, the inside of the casing 3 is largely projected from the barrel portion 3a of the casing 3 so that the space volume of the discharge chamber 7 is enlarged. In another method to enlarge the volume of the discharge chamber 7, it is however possible to attain the relative enlargement of the space volume of the discharge chamber 7 by downsizing, for example, the compressor body 4 within the interior of the casing 3 or the like. Fig. 3 shows another embodiment of the gas compressor according to the invention. The gas compressor shown in Fig. 3 is of a multi-compressor type that has two compressor bodies 4 and 4, oil separators 5 and 5 provided for each of the compressor bodies 4 and 4 and a single discharge chamber 7 commonly used for the compressor bodies 4 and 4 within the case body 1. Since the basic structure of each compressor body 4, 4 is substantially the same as that of the compressor body 4 (see Fig. 1) in the gas compressor (hereinafter referred to as a single compressor) shown in Fig. 8, the same reference numerals are used to indicate the like components and the detailed explanation therefore will be omitted. Incidentally, the space volume of the discharge chamber 7 in the multi-compressor shown in Fig. 3 corresponds to two discharge chambers 7 for the single compressor. In the multi-compressor shown in Fig. 3, the refrigerant gas of the suction chamber of each of the compressors 4 and 4 is compressed together with the oil. Then, the compressed high-pressure refrigerant gas is discharged toward the single common discharge chamber 7 after separated into the gas component and the oil component by the oil separators 5 and 5. Namely, in the multi-compressor shown in Fig. 3, the two compressor bodies 4 and 4 commonly use the single discharge chamber 7 as an object to which the high-pressure refrigerant gas is discharged. In this embodiment, the space volume of such a discharge chamber 7 (hereinafter referred to as a common discharge chamber) becomes large enough to keep a sufficient amount of oil within the gas compressor while reducing the oil circulation ratio of the air conditioning system. Incidentally, with respect to the gas component contained in the refrigerant gas discharged to the common discharge chamber 7, it passes through the condenser 10 or the like of the air conditioning system 8 and the single discharge port 7a of the case 1 in communication with the common discharge chamber 7 and returns to the suction chamber 6 through the suction port 6a to be again compressed together with the oil as the refrigerant gas. Also, with respect to the oil component contained in the refrigerant gas discharged to the common discharge chamber 7, it is temporarily reserved in the oil pool 7b at the bottom of the common discharge chamber 7 and is again compressed together with the refrigerant gas. By the way, comparing the structure in which the two single compressors are juxtaposed as shown in Fig. 8 with the single multi-compressor shown in Fig. 3, as is apparent from Figs. 2 and 3, the discharge port 7a of the case 1 may be located farther away from the oil separator 5 in the multi-compressor shown in Fig. 3. It is therefore possible to take a longer time for stagnation of the high-pressure refrigerant gas within the case 1. The amount of gravitational drop of the non-separated oil component contained in the high-pressure refrigerant gas is increased. Accordingly, the separation ability of the oil is higher in the multi-compressor. Also, in the single multi-compressor shown in Fig. 3, comparing the case where either one of the two compressor bodies 4 and 4 is operated (one side drive) with the case where the two single compressors each shown in Fig. 8 are juxtaposed and one of them is only operated, the separation ability of the oil is better in the former. This is because the space volume of the interior of the case 1 is larger in the multi-compressor; that is, the common discharge chamber 7 of the multi-compressor corresponds to the two discharge chambers 7 of the single compressors so that the time for stagnation of the high-pressure refrigerant gas within the case body 1 is longer in the multi-compressor than in the single compressor. Furthermore, in the case where the space volume of the common discharge chamber 7 of the multi-compressor in accordance with this embodiment is enlarged, the time for stagnation of the high-pressure refrigerant gas including the non-separated oil component in the common discharge chamber 7 is further elongated to be temporarily hold. Accordingly, the amount of the gravitational drop of the non-separated oil component contained in the high-pressure refrigerant gas down to the oil pool 7b at the bottom of the common discharge chamber 7 is increased. As a result, the amount of entrance of the non-separated oil component toward the condenser of the air conditioning system is considerably reduced so that the oil that inherently has nothing to do with the refrigeration is prevented from being recirculated through the air conditioning system. It is therefore possible to suppress the oil circulation ratio of the air conditioning system to a lower level and to enhance the refrigeration efficiency. Also, it is possible to reserve a sufficient amount of oil within the gas compressor and it is possible to prevent the lubrication fault of the gas compressor due to the oil shortage. Fig. 5 shows, in the case of the single compressor, a relationship between the OCR (oil circulated ratio) and a ratio of the discharge chamber space volume to the sucked gas displacement volume per one revolution of the compressor (discharge chamber space volume/sucked gas displacement volume per one revolution of the compressor). Fig. 6 shows, in the case of the multi-compressor, a relationship of the OCR and a ratio of the discharge chamber space volume to the sucked gas displacement volume per one revolution of the compressor. The combination of the oil with the refrigerant gas is PAG system oil and R22 refrigerant in both Fig. 5 and Fig. 6. It should be noted here that, with reference to Fig. 1, the sucked gas displacement volume per one revolution of the compressor means a theoretical volume of the low pressure refrigerant gas, to be sucked from the suction chamber 6 to the compressor body 4 during one revolution of the rotor 4b, which may be calculated in accordance with a dimension and a structure of the compressor body 4. Also, as described above, the OCR means the ratio of the oil component amount relative to the entire amount of the mixture of the refrigerant gas component and the oil component at any desired position within the air conditioning system except for the compressor when a part of the oil filled within the compressor is discharged to the air conditioning system by the operation of the compressor. In general, the OCR is actually measured at a portion kept in a high-pressure liquid state of the refrigerant between the condenser and the expansion valve. By the way, it is desirable that the OCR is equal to or less than a predetermined value. Namely, in, for example, the evaporator of the air conditioning system, the heat exchange is performed by causing the liquefied refrigerant condensed in the condenser from the side of the gas compressor and expanded (pressure reduction) by the expansion valve to pass through the pipe. However, in the case where the OCR is too large, it is considered that the heat transfer between the liquefied refrigerant and the wall of the pipe is hindered by a thick oil film generated on an inner wall of the pipe of the evaporator due to the excessive mixture of the amount of oil and the heat exchange efficiency would be reduced. In view of the above-described relationship between the magnitude of the OCR and the heat exchange efficiency of the air conditioning system, in experiments, it has been found that the OCR is suitable in the range of 4 % or less, that is, it may render the heat exchange efficiency of the air conditioning system to be the highest. In addition, since the multi-compressor is used in the air conditioning system into which an amount of refrigerant that is several times to several tens of times larger than that of the single compressor is sealed, in view of the cost for the sealed oil and the amount of the oil that may be sealed in the air conditioning system in an actual design, it has been found that the OCR is suitable at one percent or less. Also, although the OCR is varied in accordance with an rpm of the gas compressor, since the normal rpm of the gas compressor is around 3000 rpm, it is important that the OCR becomes suitable around this rpm. In view of the above, as is apparent from Fig. 5, in the single compressor, in the case where the rpm is at 3, 000 rpm, the OCR becomes suitable at 4% or less when the space volume of the discharge chamber 7 is two times larger than the sucked gas displacement volume per one revolution of the compressor or more. Also, as is apparent from Fig. 6, in the multi-compressor, in the case where the rpm is at 3,000 rpm, the OCR becomes suitable at one percent or less when the space volume of the discharge chamber 7 is ten times larger than the sucked gas displacement volume per one revolution of the compressor or more. Namely, in order to render the OCR to be suitable, the larger the space volume of the discharge chamber 7, the better the result will become. However, if the discharge chamber volume or the OCR is too large, the manufacture cost will be increased or the handling will be inconvenient in actually manufacturing the compressor and mounting it in the air conditioning system. In view of these factors, in the single compressor, it is most preferable that the space volume of the discharge chamber 7 is two times to ten times larger than the sucked gas displacement volume per one revolution of the compressor, and in the multi-compressor, it is most preferable that the space volume of the discharge chamber 7 is ten times to thirty times larger than the sucked gas displacement volume per one revolution of the compressor. Also, the OCR is varied in accordance with solubility between the oil and the refrigerant gas. Namely, in the case where the refrigerant gas is likely to be soluble into the oil, it is difficult to separate the gas component and the oil component even by the oil separator 5 provided in the gas compressor and the OCR within the air conditioning system tends to be high. Conversely, when the refrigerant gas is hardly dissoluble into the oil, it is easy to separate the gas component and the oil component by the oil separator 5 provided in the gas compressor and the OCR is likely to be low within the air conditioning system. Accordingly, in order to decrease the OCR, it is considered that the oil into which the refrigerant gas is hardly dissolved is selected in correspondence with the refrigerant gas to be used. However, in the case where the refrigerant gas is hardly soluble into the oil, although the amount of the oil component to be discharged into the air conditioning system 8 from the gas compressor is small per unit time, the state is at low pressure and low temperature from the outlet of the expansion valve 10 to the interior of the evaporator 11 so that the viscosity of the oil that has not been dissolved into the refrigerant gas is raised and the oil is hardly returned to the gas compressor, disadvantageously. Unless the oil is returned to the gas compressor, the amount of the oil in the oil pool 7b for lubrication of the compressor body 4 is decreased in accordance with the lapse of the operation time, resulting in the lubrication shortage for the compressor body 4. Accordingly, in order to obtain an optimum OCR without any lubrication shortage of the compressor body 4, it is important to separate the refrigerant gas component and the oil component within the gas compressor as much as possible and at the same time to establish the relationship that the refrigerant gas and the oil are soluble with each other. Here, Fig. 7 shows a relationship between the temperature and the pressure due to the difference in combination of the refrigerant gas and the oil when the refrigerant gas is dissolved into the oil by 10%. In Fig. 7, a line indicated by Go represents a border at which it is easy or difficult for the oil to return to the gas compressor in the case where the refrigerant gas is dissolved into the oil by 10%, and shows a relationship between the temperature and the pressure on the basis of which the decision is made for use of the combination of the refrigerant gas and the oil. Namely, in the combination of the refrigerant gas and the oil in which the refrigerant gas is dissolved by 10% into the oil in the range exceeding the reference value Go (the left upper region of the line indicated by Go), in particular, the pressure and temperature at the low pressure and low temperature portion of the evaporator or the like of the air conditioning system are plotted in the right lower region of the line indicated by Go. As a result, the refrigerant gas is dissolved into the oil only by less than 10%. This shows that the viscosity of the oil is increased and it is difficult for the oil to return to the gas compressor. Conversely, in the combination of the refrigerant gas and the oil in which the refrigerant gas is dissolved by 10% into the oil in the range equal to or less than the reference value Go (the right lower region of the line indicated by Go), the refrigerant gas is dissolved into the oil by 10% or more even in the low pressure low temperature portion of the evaporator or the like. This shows that it is easy for the refrigerant gas to be dissolved and it is easy for the oil to return to the gas compressor. A variety of combinations of the oil and the refrigerant gas may be proposed. For instance, as shown in Fig. 7, the easyily soluble combinations equal to or less than the reference value Go shown in Fig. 7 are: (1) PAG (polyalkylene glycol) 1 oil that is PAG system oil and R22 refrigerant, (2) PAG 2 oil that is the PAG system oil and R407 refrigerant, (3) ether oil 1 that is ether system oil and R407C refrigerant, (4) carbonate 1 oil that is carbonate system oil and R407C refrigerant, (5) carbonate 2 oil that is carbonate system oil and R410a refrigerant, (6) ester oil 1 that is ester system oil and R407C refrigerant, (7) ester 2 oil that is ester system oil and R410a refrigerant, (8) PAG 2 oil that is PAG system oil and R134a refrigerant, (9) PAG 3 oil that is PAG system oil and R134a refrigerant, and (10) PAG 4 oil that is PAG system oil and R134a refrigerant. As is apparent from Fig. 7, it is understood that in particular the combinations (1) and (8) are most easily soluble combinations out of these combinations. Incidentally, although not shown in Fig. 7, the combinations of paraffin system oil and R22 refrigerant, naphthene system oil and R134a refrigerant, and alkylbenzene system oil and R407C refrigerant may be enumerated as the combinations difficult to be dissolved between the oil and the refrigerant gas exceeding the reference value Go. Incidentally, in the foregoing embodiment, the multi-compressor provided with two compressor bodies has been described but it is apparent that the present invention may be applied to a multi-compressor having two or more compressor bodies. In the gas compressor according to the present invention, as described above, the space volume of the discharge chamber is enlarged to a large volume enough to keep the sufficient amount of oil within the gas compressor and to suppress the oil circulated ratio of the air conditioning system. For this reason, the time for stagnation of the refrigerant gas including the oil component that could not be separated by the oil separator (non-separated oil component) in the discharge chamber is elongated. Accordingly, the ratio of the non-separated oil component to drop by gravitational force down to the oil pool at the bottom of the discharge chamber is increased and the entrance amount of the non-separated oil toward the condenser of the air conditioning system is considerably reduced. As a result, a large amount of the oil that inherently has nothing to do with the refrigeration would not be circulated within the air conditioning system to enhance the refrigeration efficiency. Also, even with the combination in which the refrigerant gas is easy to be dissolved into and difficult to be separated from the oil, it is possible to suppress the oil circulated ratio within the air conditioning system and to reserve a sufficient amount of oil within the gas compressor to thereby prevent the lubrication fault of the gas compressor due to the oil shortage. The aforegoing description has been given by way of example only and it will be appreciated by a person skilled in the art that modifications can be made without departing from the scope of the present invention, as defined by the appended claims.

Claims: A gas compressor comprising: a compressor body (4) for sucking refrigerant gas and compressing the refrigerant gas together with oil for lubrication and for discharging the compressed refrigerant gas and oil; and an oil separator (5) for separating refrigerant gas after compression and discharged from said compressor body into a gas component and an oil component, characterised by further comprising: a one-piece or monolithic case (1) receiving therein said compressor body and said oil separator, the case (1) having a barrel portion (3a) having a first diameter, surrounding and contacting hermetically with a peripheral surface of said compressor body and facing and contacting hermetically with an end surface of a front head (2) which covers an end of the compressor body, characterised in that the case (1) comprises an enlarged case portion having a second diameter greater than the first diameter and extending from the barrel portion, the enlarged case portion having a discharge chamber (7) for temporarily holding the gas component and the oil component separated by said oil separator and provided with a discharge port (7a) for discharging the gas component to an air conditioning system (8) and an oil pool (7b) for receiving the oil component at a bottom with a space volume dimensioned to suppress an oil circulation ratio of the air conditioning system and to keep a sufficient amount of oil within said gas compressor body. A gas compressor according to claim 1, wherein said discharge chamber has a space volume that is two times to ten times larger than a sucked gas displacement per one revolution of said compressor body. A gas compressor according to claim 1 or claim 2, wherein the combination of the oil and the refrigerant gas is one selected from a group essentially consisting of PAG system oil and R22 refrigerant, PAG system oil and R407C refrigerant, ether system oil and R407C refrigerant, carbonate system oil and R407C refrigerant, carbonate system oil and R410a refrigerant, ester system oil and R410a refrigerant and PAG system oil and R134a refrigerant. The gas compressor according to claim 1 or claim 2 comprising a plurality of the compressor bodies (4), wherein the case (1) is arranged to receive therein the plurality of compressor bodies (4), and the discharge chamber (7) comprises a discharge chamber common to the plurality of compressor bodies (4). A gas compressor according to claim 4, wherein said common discharge chamber (7) has a space volume that is ten times to thirty times larger than a sucked gas displacement per one revolution of the said plurality of compressor bodies.

Inventors: NONAKA TAKESHI, NONAKA, TAKESHI, Nonaka, Takeshi, c/o Seiko Seiki K.K.
Applicants: SEIKO INSTR INC, SEIKO INSTRUMENTS INC.
Application year: 2000
Main classification: F04C29
IPC codes: F04C29, F04C18, F25B43, F04C23, F04B39