Rotary expansible chamber devices – Working member has planetary or planetating movement – Helical working member – e.g. – scroll
Reexamination Certificate
2000-03-09
2001-09-18
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Working member has planetary or planetating movement
Helical working member, e.g., scroll
C418S055300, C418S055400, C418S060000, C418S101000, C418S157000
Reexamination Certificate
active
06290477
ABSTRACT:
The present invention concerns a scroll vacuum pump, in particular the means allowing a certain tightness to be ensured between the moving part and the fixed part of the pump.
Scroll vacuum pumps are known in general in the state of the art. They are composed in particular of a portion of fixed housing supporting at least a first wall in the form of a scroll, and a mobile portion, supporting at least a second wall in the form of a scroll, by displacement in an orbital movement inside the said portion of housing. Since the two scrolls are interleaved one on the other, the orbital movement of the scroll mounted on the mobile portion relative to the scroll mounted on the fixed portion of housing creates a change of shape and a displacement, along the said scrolls, of a plurality of transfer chambers, each bounded by a wall portion of the fixed housing portion, of the mobile portion as well as of the two scrolls. As for a transfer chamber, its displacement thus brings a quantity of gas or air, introduced into the said chamber when this is located at one end of the said scrolls, toward the other end of the said scrolls where the said quantity of gas or air can escape. In the case where the gas or air is introduced from outside the scrolls to be drawn into the scrolls, there is a decrease in the volume of the transfer chamber between these two points, respectively an increase in the pressure of the gas or air.
The advantage of such pumps is that they can work completely dry, i.e. no lubricant comes into contact with the pumped gas or air which thus cannot be contaminated, making them particularly suitable for laboratories, the chemical industry, the food industry, etc.
One major problem with the known pumps consists in ensuring the tightness of the transfer chamber between the ridge of the fixed scroll and the wall portion of the mobile portion facing it as well as between the ridge of the mobile scroll and the wall portion of the fixed portion of casing facing it, respectively between the transfer chambers.
A known way of resolving this problem consists in allowing a slight axial movement of the mobile portion on its axis, and ensuring the tightness of the transfer chamber by arranging a joint disposed in a groove running along the ridges of the scrolls, the said joints coming into sliding contact against the walls facing them, thus leading the mobile portion in an orbital displacement so that it centers itself inside the fixed portion of casing. Owing to the sliding contact mentioned, the joint must be a friction joint, i.e. relatively rigid, respectively having only little elasticity. In order to allow dimensional adaptation of the joints to ensure the tightness of the transfer chamber, a first method consists in sandwiching a flexible joint between the bottom of the groove and the friction joint; the dimensional adaptation being produced by the flexible joint. A major drawback of this solution is its high cost. A second method consists in providing an air circulation channel between the bottom of the groove and the sliding joint, this air circulation channel having an intake orifice in a place on the scroll where the air is under relatively high pressure. One of the drawbacks of this method comes from irregularities of effect between the different operating speeds of the pump. On the other hand, and in a general way, these systems where the joints are in sliding contact with a wall result in wear and tear on the said joints, or a soiling of the transfer chamber and the necessity of frequent changing of joints as well as overheating of the walls on which the joints slide. Moreover, the tightness is not ensured in the same way between new joints and worn joints, leading to a gradual loss of performance of the pump in the course of use.
A first object of the invention is thus to propose a scroll vacuum pump not having the mentioned drawbacks of the known pumps.
To achieve this, the pump proposed avoids using joints in sliding contact on a wall; instead, a very slight play is left between the joint and the wall facing it when the pump is assembled. This first arrangement makes it possible to avoid having to install an elastic means Linder the joint. Moreover, in order to prevent the undesired effect of having the joint come into sliding contact with the wall at the wrong moment, the mobile portion is mounted on its axis so that no axial movement is possible. Thus, all the problems of friction, of wear and tear and of overheating between the fixed and mobile portions are avoided, while ensuring a sufficient tightness of the transfer chamber. A second embodiment allows completely omitting joints between the fixed and mobile portions.
Another problem relating to scroll vacuum pumps is the disequilibrium created by the mobile portion mounted eccentrically relative to the drive shaft, thus causing vibrations when the vacuum pump is functioning. In a known way, one or more counterweights adjoining the drive shaft allow a static equilibrium of the masses in rotation to be achieved. In the case of a vacuum pump whose mobile portion comprises two spiraling walls each disposed on a face of a central wall, an offsetting of one hundred eighty degrees between the two scrolls already makes it possible to diminish substantially the disequilibrium of the masses in rotation. This arrangement also has the advantage of reducing by a factor of two the gas or air depression points at the inlet of the pump, respectively the pressure points at the outlet of the pump while doubling their frequency. Nevertheless, in operation, vibrations originating from a lack of dynamic equilibrium can act upon the mobile part and not allow it to keep the play previously described between the joint and the wall facing it. In order to avoid this, the mobile portion of the vacuum pump is also balanced dynamically.
To attain the set objects, a scroll vacuum pump is proposed having the features of the main claim, variants or special embodiments being described in the dependent claims.
REFERENCES:
patent: 4990071 (1991-02-01), Sugimoto
patent: 5024589 (1991-06-01), Jetzer et al.
patent: 5209636 (1993-05-01), Fannar
patent: 5391065 (1995-02-01), Wolverton et al.
patent: 5556269 (1996-09-01), Suzuki et al.
patent: 5842843 (1998-12-01), Haga
patent: 6109897 (2000-08-01), Haga
patent: 35 38 522 A1 (1986-12-01), None
patent: 0 780 576 A2 (1997-06-01), None
patent: 3-237202 (1991-11-01), None
patent: A-5-79473 (1993-03-01), None
Ateliers Busch SA
Denion Thomas
Oliff & Berridge PLC.
Trieu Theresa
LandOfFree
Scroll vacuum pump does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Scroll vacuum pump, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Scroll vacuum pump will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2528570