US3705499A - Oil dilution control - Google Patents

Oil dilution control Download PDF

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Publication number
US3705499A
US3705499A US183127A US3705499DA US3705499A US 3705499 A US3705499 A US 3705499A US 183127 A US183127 A US 183127A US 3705499D A US3705499D A US 3705499DA US 3705499 A US3705499 A US 3705499A
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Prior art keywords
oil
temperature
refrigerant
heater
pressure
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Expired - Lifetime
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US183127A
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English (en)
Inventor
Gordon L Mount
James W Endress
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Carrier Corp
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Carrier Corp
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B31/00—Compressor arrangements
    • F25B31/002—Lubrication
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/01—Heaters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/21—Temperatures
    • F25B2700/2115—Temperatures of a compressor or the drive means therefor
    • F25B2700/21155—Temperatures of a compressor or the drive means therefor of the oil
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/21—Temperatures
    • F25B2700/2117—Temperatures of an evaporator

Definitions

  • OIL DILUTION CONTROL 721 Inventors: Gordon L. Mount, West Monroe; James W. Endress, Syracuse, both of N.Y.
  • ABSTRACT The invention has to do with a method and control mechanism for continuously maintaining a satisfactory [151 3,705,499 [451 Dec. 12, 1972 constant level of refrigerant concentration in the lubricating oil of a refrigeration compressor.
  • the method consists of continuously measuring the refrigerant pressure and the oil temperature, adjusting the oil temperature in relation to the measured refrigerant pressure to maintain a substantially constant refrigerant concentration in the oil.
  • a specific form of apparatus may consist of a thermal responsive system (as a bulb, tube, and bellows) continuously measuring the oil temperature and converting the measured temperaturevinto pressure, and a second system continuously producing a pressure commensurate to vapor pressure of the refrigerant in contact withthe oil, the pressure created by the first system acting in opposition to the pressure created by the second system to produce a force differential, as measured by the systems, for operation of a differential pressure switch means to contact and disconnect an oil heater to a power supply to maintain the vapor pressure of the oil solution at a level to limit the absorption of refrigerant in the oil solution.
  • a thermal responsive system as a bulb, tube, and bellows
  • a second system continuously producing a pressure commensurate to vapor pressure of the refrigerant in contact withthe oil, the pressure created by the first system acting in opposition to the pressure created by the second system to produce a force differential, as measured by the systems, for operation of a differential pressure switch means to contact and disconnect an oil heater to a power supply
  • oil dilution is a function of oil temperature and refrigerant pressure. It is a matter of the vapor pressures of the refrigerant and oil. Upon a decrease of oil temperature, there is a decrease in oil vapor pressure. Accordingly, if for a given refrigerant pressure, there is a decrease in oil temperature, there is an increase in refrigerant absorption.
  • One method employed to limit refrigerant absorption is to operate a heater in the oil reservoir, the heater being controlled by a thermostat set at 140 F. 'Another method is to have the heater on continuously, the heater being sized to limit oil dilution at the highest ambient temperature incurred.
  • the preferred embodiment of apparatus for carrying out our method consists of a closed thermal system such as a bulb, connected to a tube, which in turn is connected to a bellows or diaphragm, the system containing a temperature responsive fluid medium producing a variable pressure commensurate with the temperature being sensed.
  • the bulb of such a system is positioned in the oil reservoir.
  • a bulb of a like second system is located in the low side of the refrigeration apparatus.
  • the pressures created in the two sensing thermal systems act in opposition and are employed for actuation of a differential pressure operated switch serving to establish a connection between a power supply and the oil heater.
  • the temperature responsive fluid medium in one thermal system is different than the medium in the other system.
  • the media are selected to produce a differential pressure producing a curve under all conditions which will give a nearly constant level of refrigerant concentration.
  • FIG. 1 is a schematic representation of a refrigeration apparatus illustrating the control mechanism embodying our invention.
  • FIG. 2 is a graph depicting the operating curves of two fluid media that may be used in the thermal systems.
  • the refrigeration system disclosed is of the conventional arrangement including a centrifugal compressor having a frame structure 10 in which an impeller 11 is journaled and operatively connected through a gear box 12 to a driving motor mounted in a casing 13.
  • the discharge from the compressor is conveyed through a line 15 to a condenser 16.
  • the liquid refrigerant is metered through a passage 17 from the condenser to an evaporator or water chiller 18.
  • the compressor frame 10 is formed, in the base portion thereof, with an oil reservoir 19, the normal oil level being indicated by the dash line 20.
  • a heater 21 is mounted in the oil reservoir.
  • Our method consists of continuously measuring the temperature of the oil in the reservoir 19 and the pressure of the refrigerant in the low pressure area of the refrigeration system.
  • the heater 21 is powered on the basis of the measurements to maintain the temperature of the oil relative to the refrigerant pressure to establish a differential of predetermined range between the refrigerant pressure and the oil temperature. If, for example, the pressure of the refrigerant increases in respect to the oil temperature sufficiently to bring about a differential exceeding the predetermined range, the heater is operated to raise the oil temperature to a level which, at the then existing refrigerant pressure, to bring the differential within the predetermined range to prevent excessive refrigerant absorption in the oil, that is to keep the absorption of the refrigerant to a satisfactory level.
  • a thermal responsive system is used to continuously measure the temperature of the oil in the reservoir.
  • This system includes a bulb 23 positioned in the oil supply in the reservoir 19. The bulb is connected to a pressure responsive device 25 by a tube 27.
  • a like thermal responsive system is used to continuously measure the pressure of the refrigerant in the low side of the system.
  • a bulb 30 is located in a low pressure area of the refrigeration system, as in the evaporator 18, and is connected to a pressure responsive device 31 by a tube 33. The area above the oil level is included in the low pressure side of the system as by the conduit 34.
  • Each thermal system contains a quantity of fluid medium for providing a variable pressure representing a force in the system according to the temperature sensed by the bulb therein.
  • the pressure responsive devices 25, 31 are arranged in opposition and operatively connected to a movable switch contact 39. If the oil temperature is low, as sensed by the bulb 23, in comparison to the refrigerant pressure as sensed by the bulb 30, contact 39 is moved into engagement with contact 40. This results in a circuit being completed to the heater 21 from the power supply side 41, closed switch contacts 39, 40, wire 43, heater 21, wire 45, heater 21 to the side, 45 of the power supply.
  • the pressure responsive devices 25, 31 and switch contacts 39, 40 represent a conventional pressure differential operated switch. As stated above, if the refrigerant pressure applied to the device 31 exceeds the pressure applied to the device 25 by a predetermined amount, contact 39 will be moved into engagement with contact 40. It will be understood, switches of this type may be adjusted, within limits, to operate within a predetermined pressure differential or range, for example, 17 psi. Therefore, the pressure on the device 31 would have to exceed the pressure on the device 25 by 17 psi, before movement of the contact 39 into engagement with contact 40. The reverse operation is of the same order.
  • the fluids in the thermal systems are selected so as to provide a rate of variation between the force developed in one system being different from the rate of variation in the force developed in the other system, with the result that a predetermined force differential within the two systems is substantially independent of a fixed difference between the refrigerant pressure in the low side of the system and the temperature of the oil in the reservoir.
  • Fluids particularly satisfactory for use in the thermal systems have been found to be refrigerant R-l 2 and ethyl chloride, the ethyl chloride being used in the thermal system 23, 27, 25. With the use of these media, it will be understood that if the refrigeration system is being operated with refrigerant R-12, then the bulb may be omitted, that system including only the tube 33 and the responsive device 31.
  • the operation of the two thermal systems employing the refrigerant R-l2 and ethyl chloride is shown on curves on the graph in FIG. 2.
  • the operating curve for refrigerant R-l 2 is shown at 41 and the curve for ethyl chloride is shown at 42. It will be observed that these curves show the non-linear saturation pressures for the respective fluids and that the curves diverge with increase in temperature.
  • the vapor pressure of the refrigerant is 85 psia, as shown at the intersecting point 43 of line 44 with the R-l2 curve 41.
  • the vapor pressure of the ethyl chloride is 20 psia as shown at the intersecting point 45 of line 44 with the ethyl chloride curve 42.
  • the vapor pressure of the refrigerant is 173 psia as determined at the intersecting point between the line 51 and the R- 12 curve 41.
  • the oil is heated to a temperature of 204 F as determined by the intersecting point 53 by the line 55 and the ethyl chloride curve 42. 4
  • thermal systems referred to provide a particularly satisfactory and efficient means for continuously measuring the oil temperature and the refrigerant vapor pressure, it will be apparent other systems and devices may be employed for the purpose.
  • the method of maintaining a substantially constant level of refrigerant concentration in the lubricating oil supply or the compressor of a refrigeration system comprising the steps of continuously measuring the refrigerant vapor pressure, continuously measuring the temperature of the oil supply, and adjusting the temperature of the oil supply in relation to the measured refrigerant vapor pressure to maintain a differential, within a predetermined range, between the measured vapor pressure of the refrigerant and the measured temperature of the oil supply.
  • a refrigeration apparatus including a refrigerant compressor having a lubricating oil reservoir containing a supply of lubricating oil and a control mechanism for maintaining a substantially constant level of refrigerant concentration in the lubricating oil, said control mechanism comprising an oil heater mounted in heat exchanging relation with the oil in said reservoir, said heater being operable when energized to raise the oil temperature, sensing means continuously sensing the refrigerant vapor pressure and oil temperature, and heater energizing means for energizing said heater in response to said sensing means sensing a differential, exceeding a predetermined range, between saidrefrigerant vaporpressure and oil temperature.
  • a refrigeration apparatus including a refrigerant compressor having a lubricating oil reservoir containing a supply of lubricating oil and a control mechanism for maintaining a substantially constant level of refrigerant concentration in the lubricating oil, said control mechanism comprising an oil heater mounted in heat exchanging relation with the oil in said reservoir, a power supply for operating said heater to raise the temperature of the oil in said reservoir, means operable to continuously produce a signal indicative of the vapor pressure of the refrigerant contacting the oil in said' oil reservoir, a temperature sensing means operable to continuously produce a signal indicative of the temperature of the oil in said reservoir, and heater v control means responsive upon the sensed refrigerant pressure signal exceeding the sensed oil temperature signal by a predetermined amount to connect said heater to said power supply.
  • a refrigeration system including a refrigerant compressor having a lubricating oil reservoir and control mechanism for maintaining a substantially constant level of refrigerant concentration in the compressor lubricating oil, said control mechanism comprising a heater mounted in said oil reservoir, a power supply for operating said heater to raise the temperature of the oil in said reservoir, a first measuring means for continuously measuring the vapor pressure of the refrigerant contacting the oil in said reservoir, a second measuring means for continuously measuring the temperature of the oil in said reservoir, and heater control means responsive to a differential exceeding a predetermined range, as measured by said first and second means, to connect said heater to said power supply to maintain a substantially constant level of refrigerant concentration in said oil supply.
  • Refrigeration apparatus including a compressor having a lubricating oil reservoir containing supply of lubricating oil and control mechanism for maintaining a constant level of refrigerant concentration in the compressor lubricating oil; said control mechanism comprising a heater mounted in heat exchanging relation to the oil in said oil reservoir; a power supply for said heater; a first thermal responsive system containing a temperature responsive fluid medium for producing a variable pressure representing a force within said system; said system sensing the temperature in the low side of said refrigeration system; a second thermal responsive system containing a temperature responsive fluid medium different from said first fluid medium for producing a variable pressure representing a force within said second system; said second system sensing the temperature of the oil in said reservoir; the force created by expansion of .fluid within the first system acting in opposition to the force created by expansion of fluid within the second system, and the rate of variation between the force and temperature in said first system being different from the rate of variation between the force and temperature in said second system so that a predetermined force differential within the two systems is substantially independent of a fixed temperature difference
  • a control mechanism as set forth in claim 1 wherein said means responsive to said predetermined force differential consists of a pressure operated switch operable when actuated by said force differential to tially filled with ethyl chloride.
  • ABSTRACT line 19
  • cancel "contact” and insert in place Column 4, line 48,.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Control Of Positive-Displacement Pumps (AREA)
  • Lubricants (AREA)
  • Control Of Temperature (AREA)
US183127A 1971-09-23 1971-09-23 Oil dilution control Expired - Lifetime US3705499A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US18312771A 1971-09-23 1971-09-23

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US3705499A true US3705499A (en) 1972-12-12

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US183127A Expired - Lifetime US3705499A (en) 1971-09-23 1971-09-23 Oil dilution control

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US (1) US3705499A (enrdf_load_stackoverflow)
JP (1) JPS5232115B2 (enrdf_load_stackoverflow)
CA (1) CA960332A (enrdf_load_stackoverflow)
DE (1) DE2246541C3 (enrdf_load_stackoverflow)
FR (1) FR2153429A1 (enrdf_load_stackoverflow)
IT (1) IT967559B (enrdf_load_stackoverflow)

Cited By (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4208883A (en) * 1977-07-18 1980-06-24 The Electricity Council Compressors for heat pumps
US4671081A (en) * 1985-02-06 1987-06-09 Satoru Fujiwara Device for collecting lubricating oil in a turbo-refrigerator
FR2618537A1 (fr) * 1987-07-24 1989-01-27 Unite Hermetique Sa Motocompresseur hermetique a securite amelioree
US4912938A (en) * 1989-07-28 1990-04-03 American Standard Inc. DC voltage bleeder for a variable speed air conditioner
US5012652A (en) * 1990-09-21 1991-05-07 Carrier Corporation Crankcase heater control for hermetic refrigerant compressors
US5040382A (en) * 1990-06-19 1991-08-20 501 Wynn's Climate Systems, Inc. Refrigerant recovery system
US5265432A (en) * 1992-09-02 1993-11-30 American Standard Inc. Oil purifying device for use with a refrigeration system
US5469713A (en) * 1994-01-21 1995-11-28 Skf Usa, Inc. Lubrication of refrigerant compressor bearings
WO2000017586A1 (en) * 1998-09-22 2000-03-30 American Standard Inc. Refrigeration apparatus including an oil sump heater
EP1014243A1 (en) * 1998-12-21 2000-06-28 Texas Instruments Incorporated Differential oil pressure control apparatus and method
US20070006608A1 (en) * 2003-07-29 2007-01-11 Lee Deok-Jae Oil checking device for compressor of air conditioning system
US20120210742A1 (en) * 2009-11-11 2012-08-23 Mitsubishi Electric Corporation Air-conditioning apparatus
CN103089577A (zh) * 2011-11-04 2013-05-08 艾默生环境优化技术公司 用于压缩机的油管理系统
EP2781855A4 (en) * 2011-09-30 2015-09-16 Daikin Ind Ltd COOLER
US9181939B2 (en) 2012-11-16 2015-11-10 Emerson Climate Technologies, Inc. Compressor crankcase heating control systems and methods
US9353738B2 (en) 2013-09-19 2016-05-31 Emerson Climate Technologies, Inc. Compressor crankcase heating control systems and methods
US9810218B2 (en) 2009-09-24 2017-11-07 Emerson Climate Technologies Crankcase heater systems and methods for variable speed compressors
US9897360B2 (en) * 2013-03-08 2018-02-20 Daikin Industries, Ltd. Refrigeration apparatus
US10119734B2 (en) 2004-11-05 2018-11-06 Arcelik Anonim Sirketi Cooling device with compressor cabinet heater and a control method
US10132542B2 (en) 2012-11-29 2018-11-20 Johnson Controls Technology Company Pressure control for refrigerant system
US11073313B2 (en) 2018-01-11 2021-07-27 Carrier Corporation Method of managing compressor start for transport refrigeration system
US11435125B2 (en) 2019-01-11 2022-09-06 Carrier Corporation Heating compressor at start-up
US11624539B2 (en) 2019-02-06 2023-04-11 Carrier Corporation Maintaining superheat conditions in a compressor

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE385801B (sv) * 1974-03-27 1976-07-26 B Weideskog Elektriskt driven rakapparat
JPH0483021U (enrdf_load_stackoverflow) * 1990-11-30 1992-07-20

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2175913A (en) * 1935-12-18 1939-10-10 Nash Kelvinator Corp Motor-compressor unit for refrigerating apparatus
US3208237A (en) * 1957-09-27 1965-09-28 Carrier Corp Refrigerating apparatus
US3336762A (en) * 1966-03-02 1967-08-22 Tri State Engineering & Sales Refrigeration method and apparatus for lubricant handling
US3411313A (en) * 1966-12-02 1968-11-19 Carrier Corp Compressor protective control
US3543880A (en) * 1969-07-07 1970-12-01 Vilter Manufacturing Corp Two stage refrigeration compressor having automatic oil drain for the first stage suction chamber

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2175913A (en) * 1935-12-18 1939-10-10 Nash Kelvinator Corp Motor-compressor unit for refrigerating apparatus
US3208237A (en) * 1957-09-27 1965-09-28 Carrier Corp Refrigerating apparatus
US3336762A (en) * 1966-03-02 1967-08-22 Tri State Engineering & Sales Refrigeration method and apparatus for lubricant handling
US3411313A (en) * 1966-12-02 1968-11-19 Carrier Corp Compressor protective control
US3543880A (en) * 1969-07-07 1970-12-01 Vilter Manufacturing Corp Two stage refrigeration compressor having automatic oil drain for the first stage suction chamber

Cited By (33)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4208883A (en) * 1977-07-18 1980-06-24 The Electricity Council Compressors for heat pumps
US4671081A (en) * 1985-02-06 1987-06-09 Satoru Fujiwara Device for collecting lubricating oil in a turbo-refrigerator
FR2618537A1 (fr) * 1987-07-24 1989-01-27 Unite Hermetique Sa Motocompresseur hermetique a securite amelioree
US4912938A (en) * 1989-07-28 1990-04-03 American Standard Inc. DC voltage bleeder for a variable speed air conditioner
US5040382A (en) * 1990-06-19 1991-08-20 501 Wynn's Climate Systems, Inc. Refrigerant recovery system
US5012652A (en) * 1990-09-21 1991-05-07 Carrier Corporation Crankcase heater control for hermetic refrigerant compressors
US5265432A (en) * 1992-09-02 1993-11-30 American Standard Inc. Oil purifying device for use with a refrigeration system
US5469713A (en) * 1994-01-21 1995-11-28 Skf Usa, Inc. Lubrication of refrigerant compressor bearings
WO2000017586A1 (en) * 1998-09-22 2000-03-30 American Standard Inc. Refrigeration apparatus including an oil sump heater
EP1014243A1 (en) * 1998-12-21 2000-06-28 Texas Instruments Incorporated Differential oil pressure control apparatus and method
US6237420B1 (en) 1998-12-21 2001-05-29 Texas Instruments Incorporated Differential oil pressure control apparatus and method
US20070006608A1 (en) * 2003-07-29 2007-01-11 Lee Deok-Jae Oil checking device for compressor of air conditioning system
US7347061B2 (en) * 2003-07-29 2008-03-25 Metachem Inc. Oil checking device for compressor of air conditioning system
US10119734B2 (en) 2004-11-05 2018-11-06 Arcelik Anonim Sirketi Cooling device with compressor cabinet heater and a control method
US9810218B2 (en) 2009-09-24 2017-11-07 Emerson Climate Technologies Crankcase heater systems and methods for variable speed compressors
US20120210742A1 (en) * 2009-11-11 2012-08-23 Mitsubishi Electric Corporation Air-conditioning apparatus
US9528733B2 (en) * 2009-11-11 2016-12-27 Mitsubishi Electric Corporation Air-conditioning apparatus
EP2781855A4 (en) * 2011-09-30 2015-09-16 Daikin Ind Ltd COOLER
US9939184B2 (en) 2011-09-30 2018-04-10 Daikin Industries, Ltd. Refrigeration device
CN103089577A (zh) * 2011-11-04 2013-05-08 艾默生环境优化技术公司 用于压缩机的油管理系统
CN103089577B (zh) * 2011-11-04 2016-04-27 艾默生环境优化技术公司 用于压缩机的油管理系统
US9551357B2 (en) 2011-11-04 2017-01-24 Emerson Climate Technologies Gmbh Oil management system for a compressor
EP2589898A3 (en) * 2011-11-04 2014-01-15 Emerson Climate Technologies GmbH Oil management system for a compressor
US10801764B2 (en) 2012-11-16 2020-10-13 Emerson Climate Technologies, Inc. Compressor crankcase heating control systems and methods
US9851135B2 (en) 2012-11-16 2017-12-26 Emerson Climate Technologies, Inc. Compressor crankcase heating control systems and methods
US9181939B2 (en) 2012-11-16 2015-11-10 Emerson Climate Technologies, Inc. Compressor crankcase heating control systems and methods
US10132542B2 (en) 2012-11-29 2018-11-20 Johnson Controls Technology Company Pressure control for refrigerant system
US9897360B2 (en) * 2013-03-08 2018-02-20 Daikin Industries, Ltd. Refrigeration apparatus
US9879894B2 (en) 2013-09-19 2018-01-30 Emerson Climate Technologies, Inc. Compressor crankcase heating control systems and methods
US9353738B2 (en) 2013-09-19 2016-05-31 Emerson Climate Technologies, Inc. Compressor crankcase heating control systems and methods
US11073313B2 (en) 2018-01-11 2021-07-27 Carrier Corporation Method of managing compressor start for transport refrigeration system
US11435125B2 (en) 2019-01-11 2022-09-06 Carrier Corporation Heating compressor at start-up
US11624539B2 (en) 2019-02-06 2023-04-11 Carrier Corporation Maintaining superheat conditions in a compressor

Also Published As

Publication number Publication date
IT967559B (it) 1974-03-11
DE2246541C3 (de) 1979-10-18
CA960332A (en) 1974-12-31
DE2246541B2 (de) 1979-01-18
JPS4840038A (enrdf_load_stackoverflow) 1973-06-12
FR2153429A1 (enrdf_load_stackoverflow) 1973-05-04
DE2246541A1 (de) 1973-03-29
JPS5232115B2 (enrdf_load_stackoverflow) 1977-08-19

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