A New Mechanical Oil Sensor Technology

Transcription

1 Purdue Uiversity Purdue e-pubs Iteratioal Compressor Egieerig Coferece School of Mechaical Egieerig 01 A New Mechaical Oil Sesor Techology Weihua Guo warer.guo@emerso.com Qiag Liu Ruiqiag Wag Hogsha Li Follow this ad additioal works at: Guo, Weihua; Liu, Qiag; Wag, Ruiqiag; ad Li, Hogsha, "A New Mechaical Oil Sesor Techology" (01). Iteratioal Compressor Egieerig Coferece. Paper This documet has bee made available through Purdue e-pubs, a service of the Purdue Uiversity Libraries. Please cotact epubs@purdue.edu for additioal iformatio. Complete proceedigs may be acquired i prit ad o CD-ROM directly from the Ray W. Herrick Laboratories at Herrick/Evets/orderlit.html

2 1338, Page 1 A New Mechaical Oil Sesor Techology Guo, Weihua; Liu, Qiag; Wag, Ruiqiag; Li, Hogsha Research & Developmet Ceter, Emerso Climate Techologies (Suzhou) Co., Ltd., Iteratioal Sciece Park 1355 Jijihu Aveue, Suzhou, Jiagsu, Chia Tel: (86) Fax: (86) warer.guo@emerso.com qiag.liu@emerso.com ruiqag.wag@emerso.com hosu.li@emerso.com ABSTRACT I view of disadvatages of commercially available oil level sesig products, this paper itroduces a ew mechaical type of oil sesor for refrigeratio compressor s oil level protectio, which is used to avoid failure due to lack of oil i the compressor, especially whe multi-compressors were coected i parallel. The paper aalyzed this ew mechaical oil seor i terms of superiority comparig with other type oil sesor, theoretical workig priciple, desig cocept, fuctioal test ad typical applicatio o multi-compressors system. The method of istallatio ad the system cotrol logic are also discussed. Key words: Mechaical-Oil sesor, Oil level, Multiple Compressor Applicatio 1. INTRODUCTION The air coditioig uit with multi-compressors coected i parallel is widely used i the commercial refrigeratio ad air-coditioig field due to its high seasoal EER, improved coveiece o maiteace. As to such multi-compressors uit, the oil balace betwee differet compressors is a key poit to esure every compressor with good oil lubricatio therefore the system maitais superior reliability. A lot of efforts have bee doe to retai eough oil i each compressor whe the compressor is ruig. The popular method is to use the oil level sesor, icludig magetic reed switch oil level sesor, optical oil level sesor, as well as hall effective oil level sesor. These types of sesor fuctio are well i ormal coditios, but with the ruig of compressor, some debris happeed ad oil physical parameter slightly chaged due to moisture ad miscibility with refrigerat these types of sesor sigal accordig to sese oil physical parameter could have big sigal variatio. I additio, the cost is high because of the complexity of the sesor desig. This paper maily discusses the ew mechaical oil level sesor techology ad its operatio priciples, through comparig to these commercially available oil sesor, i terms of cost, sigal stability ad reliability. The fuctioal test results ad typical applicatios o the system have also bee preseted.. DESIGN CONCEPT This ew mechaical oil sesor is a mechaism which is used to judge whether the oil level i compressor is safe by directly detectig oil i shaft by sesig oil pressure, ormally the oil pressure i shaft is very low. The key techology of mechaical oil sesor is how to set up a relatio betwee oil pressure ad oil level, ad desig simple mechaism to build eough oil pressure to trigger sigal to system cotrol board.1 Theoretical Aalysis Figure 1 illustrates the origi of pressure differece. Whe compressor shaft rotates at agular velocity, oil droplet will produce radial velocity v due to the cetrifugal force as show i figure 1(a). Iteratioal Compressor Egieerig Coferece at Purdue, July 16-19, 01

3 1338, Page (a) (b) Figure 1: The Diagram Of How Liquid Droplets Speed Up Due To Cetrifugal Force v ca be deduced from the followig equatio. dr v dt dv r dt v v v 0 r r The oil droplets speeds up from poit 1 to poit due to cetrifugal force as show i figure 1(b). Its kietic eergy will be chaged as E E E 0 v v0 r r v dv 0 ( v 0 0) The oil droplet's kietic eergy ca be coverted ito oil pressure, the differetial pressure betwee poit1 ad poit is as below: v v 1 r0 (1-1) (1-) P ρe m ρ (1-3) Assumig that poit 1 is o the ceter axial of compressor shaft ad it has o radial velocity. The value of pressure diffidece ca be gaied from equatio (1-1) ad (1-3) r r r dr mv E1 mv1 P ρe m ρ (1-4) From equatio (1-4), it ca be see that the value of pressure differece depeded o r, ρ ad. These are the origial ad domiatig parameters for delta pressure. The oil paraboloid will be geerated i the shaft due to the rotatio of shaft, as show i the figure1 (b).the shape of oil paraboloid depeds o the agular velocity of shaft, ad the positio of oil paraboloid depeds o the oil level i compressor. There are o oil droplets eterig ito Tube, Whe r > ( r 1 l), ad it mea there is o differetial pressure betwee poit1 ad piot, vice verse, because there will be o oil left iside the tube. If the compressor desig is fixed, its radius of rotatio r, agular velocity ad desity of lubricatio ρ are fixed, pressure differece betwee poit 1 ad poit depeds o the legth of tube ad oil level iside the compressor. Iteratioal Compressor Egieerig Coferece at Purdue, July 16-19, 01 p

4 1338, Page 3 Whe the tube legth is fixed ad the oil level is sufficiet, the value of pressure diffidece is more or less costat. If the tube legth is determied, the jump poit depeds o the oil level i the compressor as show i the figure 3. Figure : Relatioship Betwee Height Of Oil Level Ad Pressure Differece Figure 3 illustrates the relatioship betwee the height of oil level iside the oil sump ad the legth of tube. Whe higher oil pressure is eeded i the oil groove, the loger of the legth of tube, the higher of the height of oil level we eed i the compressor, it meas that there is a certai relatioship betwee the legth of tube ad the height of oil level i the compressor. Figure 3: Relatioship Betwee The Height Of Oil Level Ad The Legth Of Tube. Oil Pressure Switch Mechaical Desig Theoretical aalysis gives the relatio betwee oil level ad oil pressure jump poit, ad eough oil pressure differece. Oil mechaical sesor structure desig focus o how to use this oil pressure differece to trigger the sigal ad sed the sigal to system cotrol board as figure 3, the pressure switch mechaism structure will be used as Figure 4, ad Figure 5. Whe pumpig oil, oil flows through the tube ad gets ito low bearig groove, oil sesig pressure will be built up by cetrifugal force. Oil sesig pressure pushes pisto to close cotact electrodes to sed out a oil presece sigal, sprig force pushes pisto back to ope cotact electrodes to sed out lack of oil sigal. Iteratioal Compressor Egieerig Coferece at Purdue, July 16-19, 01

5 1338, Page 4 (a) (b) Figure 4: Mechaical Oil Sesor Structure Ad Workig Process Diagram Figure 5: Mechaical Oil Sesor Workig Priciple Diagram 3. FUNCTIONAL TEST Oe compressor with the mechaical oil sesor is built for testig. The sesor sigal was recorded whe the compressor starts/stops, to determie whether or ot the compressor lacks of oil. As show i figure 6, whe the compressor starts-up with ormal oil level, poit a ad poit b of mechaical oil sesor coects, ad the sesor seds out ormal oil level sigal. Whe the oil level decrease below the protected oil level, poit a ad poit b of mechaical oil sesor discoects, seds out lack of oil sigal. 3.1 Fuctioal Test Setup Figure 6: Mechaical Oil Sesor Protected Oil Level Use scroll compressor which is built with the mechaical oil sesor. Two valves are used to chage the oil level whe the compressor is ruig. As show i Figure 7, use valve 1 to add oil ito the compressor to icrease the oil Iteratioal Compressor Egieerig Coferece at Purdue, July 16-19, 01

6 1338, Page 5 level ad valve to remove oil from oil sump i compressor to decrease oil level. The mechaical oil sesor sigal detectig circuit is show as figure 5, which is used for catchig the sesor s sigal whe compressor is ruig 3. Test Results Figure 7: The Fuctioal Test Method ad Sesor Sigal Detectig Circuit Whe the compressor starts-up with ormal oil level, poit a ad poit b of the mechaical oil sesor closes, the sesor sigal is show i figure 8, about 0.1s delay after compressor start up. This respose time is acceptable for applicatio o compressor oil protectio Figure 8: Mechaical Oil Sesor Sigal Whe Compressor Starts-up Whe the oil level iside the compressor is lower tha protected oil level, poit a ad poit b of mechaical oil sesor opes, seds out lack of oil sigal, as show i figure 9. This sigal is very steady ad is friedly to use for system logical cotrol Figure 9: Mechaical Oil Sesor Sigal Whe Compressor Lack Of Oil Iteratioal Compressor Egieerig Coferece at Purdue, July 16-19, 01

7 1338, Page 6 Whe the compressor stops, poit a ad poit b of mechaical oil sesor opes, the sesor sigal is show as figure 10. Figure 10: Mechaical Oil Sesor Sigal Whe Compressor Stops 4. TYPICAL APPLICATION This ew mechaical oil sesor is applicable to multi split AC system (as show i figure 11). The ew mechaical oil level sesor is a switch. Whe a idividual compressor starts with ormal oil level, the switch will close. Whe the oil level decreases below the protected oil level, the switch opes, a time delay starts (due to the oil level is dyamic whe compressor is ruig), ope the soleoid valve, brigs more oil ito this compressor. Whe the oil level returs above the protected oil level, the switch closes, delay some time (i order to charge oil to ormal oil level), close the soleoid valve to complete the cycle. Typical applicatio logic i the system is show i the figure 1. It is worth otig that the mechaical oil sesor oly detects liquid level iside the compressor, ad it could t idetify whether or ot the liquid refrigerat mixed with the oil, so the liquid-back cotrol logic is still eeded i the system, as it is popular today o these commercial heat pumps ad refrigeratio systems. 1 commo suctio commo discharge 3 codeser 4 oil filter 5 oil separator Figure 11: Mechaical Oil Sesor Typical Applicatio System Iteratioal Compressor Egieerig Coferece at Purdue, July 16-19, 01

8 1338, Page 7 Figure 1: Typical Applicatio Logic I The System 5. SUMMARY A ew mechaical oil sesor is discussed from the theoretical aalysis ad structure desig. The sesor sigal durig compressor start/stop ad lack of oil coditio are tested o a sample compressor with the mechaical oil sesor built-i. The mechaical oil sesor techology which is discussed i this paper has obvious advatages, such as simplified structure, lower cost, high sigal stability ad reliability ad simplified cotrol logic. It is a promised solutio to make a reliable oil balace o multi-compressor system ad therefore the overall system reliability is improved. r v r 6. NOTE OF EQUATION - The distace betwee oil droplet ad the ceter lie of compressor shaft -Radius velocity of oil droplet -Agular velocity of compressor shaft 0 -The origial distace betwee oil droplet ad the ceter lie of compressor shaft m -The mass of oil droplet E -The differetial kietic eergy betwee poit 1 ad ρ -The desity of oil lubricatio P -The differetial pressure betwee poit 1 ad -The kietic eergy of poit E E 1 v v 1 - The kietic eergy of poit 1 -The radius velocity of poit -The radius velocity of poit 1 Iteratioal Compressor Egieerig Coferece at Purdue, July 16-19, 01

9 1338, Page 8 r 1 l H -The radius of compressor shaft rotatio - The legth of tube -The height from the bottom of compressor shaft to the ceter of tube r -The distace betwee ceter compressor shaft ad the poit o oil paraboloid at H height p Iteratioal Compressor Egieerig Coferece at Purdue, July 16-19, 01