Vacuum pump

Abstract: This invention relates to a vacuumpump. The pump comprises a pump housing (10) having an upper and a lower cylindical, partly liquid filled, compression chamber (11 and 12 resp.) which are separated from each other and in which an upper and a lower part (14, 15) of a piston (12) is movable. The piston has a passage (21) which is provided with a check valve and which is a communication between the upper and the lower chamber (11 and 12 resp.). The upper chamber communicates via an opening (26) which is provided with a check valve with a liquid filled deaeration receptacle (27) whereas the lower chamber (12) during a part of the movement of the piston via an inlet (33) communicates with the space being evacuated.

Description: This invention relates to a vacuum pump. The pump according to the invention is primarily used to create a vacuum insulation for walls and doors for refrigerators and freezers. Previosly suggested vacuum insulations for this purpose - see for instance SE-A-90937, EP-A-188806, US-A-4668555 - comprise powder- or cellular materials which are placed in a diffusion tight receptacle which is evacuated and sealed before it is placed in the wall or door panel of the refrigerator or freezer. It is however time consuming to continue with the evacuation procedure as long as should be desirable which means that the procedure is not particularly well suited for mass production. There also is a risk that a leakage arises in the diffusion tight layer during the life time of the refrigerator, which is abt. 15 - 20 years, and which means that the contribution which the vacuum gives to the insulation capability disappears. In order to create vacuum for this type of equipment conventional vacuum pumps are used. For instance DE-C-157471 describes a one step evacuation pump having a piston reciprocating in a cylinder the cylinder and piston being provided with a check valve system by means of which the air is evacuated through an oil reservoir to the atmosphere whereas the oil is partly returned to the lower part of the pump where it is used to eliminate the dead space. However, this type of vacuum pumps are expensive, large, comparatively power demanding and can not be used to evacuate water vapour or to continue the evacuation procedure particularly far. The purpose of this invention is to achieve a two step vacuum pump which is to be installed permanently in a refrigerator or a freezer in order to create a vacuum in the walls and the door of the cabinet when the cabinet is started up. Since the pump has a low energy consumption, is cheap when being produced, can pump water vapour and establishes a high degree of evacuation when being connected for a long period the pump is very well suited for this purpose. The advantages mentioned above are achieved because the invention has the caracteristics mentioned in the claims. An embodiment of the invention will now be described with reference to the accompanying drawing on which fig 1-2 is a vertical section through the pump under different operating conditions. In the figures 10 is a pump housing in which there is an upper and a lower cylindric compression chamber 11 and 12 resp. Between the two chambers there is a piston 13 having an upper part 14 and a lower part 15 which during the upwards and downwards movement of the piston each slides in one of the chambers the lower part having a larger diameter than the upper part. The bottom area 16 of the lower chamber has a mainly conical shape with three step shaped portions 17, 18, 19 being parts of cones with different top angles. The piston 13 has a recess 20 with a corresponding conical shape which in its upper part via an opening 21 enters into a central, vertical channel 22 which is a communication between the two chambers 11, 12. The lower part of the channel is shaped as a valve seat in which a valve body 23 such as a ball rests. The tip of the portion 19 has such a shape that it, when the piston 13 is in its lower position, lifts the valve body 23 from the seat. Also the top area 24 of the upper chamber 11 as well as the uppermost part 25 of the piston 13 have a mainly conical shape the upper chamber 11 via an opening 26 communicating with a deaeration receptacle 27 containing a liquid preferably oil. The lower part of the deaeration receptacle is shaped as a valve seat in which a valve body 28 such as a ball normally rests. The valve body 28 is in the uppermost position of the piston lifted by means of a lifting element 29 which is arranged at the upper part 14 of the piston 13 this element also keeping the valve body 28 in its position in the channel 22. The lower part 15 of the piston 13 is connected to driving means shaped as rods 30, of which one is shown in the figures, the rods extending through the pump housing 10 and the deaeration receptacle 27. The up and down movement of the rods is achieved by means of a transmission mechanism 31 which is not shown in detail in the figures and an electric drive motor 32 for instance a syncronous motor. The pump housing also has an inlet 33 which communicates with the space being evacuated and this inlet also communicates with the chamber 12 via a passage 34 when the piston 12 is close to its upper dead point. The lower part 15 of the piston 12 has an opening 35 which extends from its bottom side to its upper side and the lower part of which is provided with a mesh net 36 covering the opening and preferably having a mesh size of 10-50 µm and which is covered by oil. This arrangement, because of the surface tension of the oil, operates as a power restricting valve decreasing the top load on the drive motor 32 during the downwards movement of the piston 13 and admits gas to flow upwards through the mesh net 36 under a suitable flow resistance but restricts the flow of oil in the same direction because of a considerably higher flow resistance. The pump operates in the following way. In fig 1 the piston 13 is shown at its upper dead point which means that the passage 34 connecting the inlet 33 with the chamber 12 is open. Shortly after the piston 13 has started its downwards movement by means of the motor 32, the transmission mechanism 31, and the rods 30 the passage 34 is closed by means of the piston 13 and the compression of the gas which is present in the chamber 12 starts. The space below the piston is thus reduced and the oil which is present on the bottom of the chamber is together with the gas which is present above the oil pressed up towards the opening 21. When the pressure in the chamber 12 exceeds the pressure in the chamber 11 or when the tip of the portion 19 lifts the valve body 23 from the seat, see fig 2, gas and oil is pressed upwards into the channel 22. Under certain conditions gas and a part of the oil also flows through the fine mesh net 36 and up through the oil layer above and thus limits the power consumtion for the pump. When the piston 13 from the position shown in fig 2 moves upwards a minor quantity of oil will flow back to the chamber 11 after which the valve body 23 returns back to the seat and prevents the oil from flowing back to the chamber 12 at the same time as the gas which is present above the oil in the chamber 11 is compressed. When the pressure in the chamber 11 is sufficiently large or when the element 29 reaches the valve body 28 the valve body moves away from the seat which means that the gas and possibly a part of the oil leaves to the deaeration receptacle 27 from which the gas then leaves to atmosphere. Simultaneously gas again flows through the passage 34 to the chamber 12 after which the procedure mentioned above is repeated. It should be observed that the pump demands a very small mechanical power which means less than 1 W and preferably less than 0,1 W and that the pump therefore is well suited to be used in a refrigerator or a freezer in order to evacuate the wall panels for a long period which in this context means more than one week. The evacuation procedure thus goes very far and a pressure is created which is less than 1 mbar preferably less than 0,1 mbar. The suggested design of the pump also makes it possible to pump water vapour which usually is a problem for vacuum pumps. It is also possible to return the oil from the deaeration receptacle 27 to the lower chamber 12 by using a larger gap between the rods 30 and the housing 10. The mesh net 36 in the power limiting valve can also be replaced by other similar arrangements for instance by several through holes with such a small diameter that the capillaray forces and the surface tension of the oil gives the intended effect.

Claims: Vacuumpump, comprising a pump housing (10) having an upper and a lower cylindical, partly liquid filled, compression chamber (11 and 12 resp.) which are separated from each other and in which an upper and a lower part (14,15) of a piston (13) is movable, the piston having a passage (21) which is provided with a check valve and which is a communication between the upper and the lower chamber (11 and 12 resp.), the upper chamber via an opening (26) which is provided with a check valve communicating with a liquid filled deaeration receptacle (27) and the lower chamber (12) during a part of the movement of the piston via an inlet (33) communicating with the space being evacuated. Vacuumpump according to claim 1, caracterized in that the upper chamber (11) has less diameter than the lower chamber (12). Vacuumpump according to claim 1 or 2, caracterized in that the bottom surface (16) of the lower chamber (12) has a mainly conical shape and that the piston (13) has a central recess (20) with a shape corresponding to the bottom surface (16). Vacuumpump according to claim 3, caracterized in that the bottom surface (16) is step shaped the different steps (17, 18, 19) having different top angles. Vacuumpump according to any of the preceding claims, caracterized in that the top surface (24) of the upper chamber (11) has a mainly conical shape and that the upper part (14) of the piston (13) has a corresponding shape. Vacuumpump according to any of the preceding claims, caracterized in that the communication (34) between the inlet (33) and the lower chamber (12) is so arranged that it is opened when the piston reaches its upper position. Vacuumpump according to any of the preceding claims, caracterized in that the piston (13) is connected to at least one drive means (30) preferably a rod which extends through the liquid which is present in the deaeration receptacle (27). Vacuumpump according to any of the preceding claims, caracterized in that the lower part (15) of the piston (13) is provided with at least one opening (35) or the like which connects the lower chamber (12) with the inlet (33) the opening forming a power limiting valve. Vacuumpump according to claim 8, caracterized in that the valve comprises a fine mesh net (36) covering the opening and preferably having a mesh size of 10 - 50 µm. Vacuumpump according to any of the preceding claims, caracterized in that it via a movement transmission mechanism (31) is connected to an electric drive motor (32), for instance a synchronus motor, the mechanical power of the pump not exceeding 1 W and preferably being less than 0,1 W. Vacuumpump according to any of the preceding claims, caracterized in that it is used to evacuate wall or a door panels in a refrigerator or freezer. Vacuumpump according to any of the preceding claims, caracterized in that it comprises one or several means (19,29) for lifting one of the valve bodies (23,28) near the upper and/or lower dead point of the piston.

Inventors: HAEGERMARCK ANDERS, HAEGERMARCK, ANDERS
Applicants: ELECTROLUX RES & INNOVATION, ELECTROLUX RESEARCH & INNOVATION AB
Application year: 1993
Main classification: F04B37
IPC codes: F04B37