Pumps – With condition responsive pumped fluid control – Pressure responsive relief or bypass valve
Reexamination Certificate
1999-11-24
2002-03-26
Freay, Charles G. (Department: 3746)
Pumps
With condition responsive pumped fluid control
Pressure responsive relief or bypass valve
C418S201300
Reexamination Certificate
active
06361289
ABSTRACT:
CROSSREFERENCE OF PENDING APPLICATION
This application is 371 of pending international application PCT/EP98/03601 filed on Jun. 15, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a medical gear pump for suction and irrigation, in particular for endoscopy or the laboratory, comprising two meshing gears as conveying elements, one of which is joined to a drive mechanism, the gears being received in cylindrical openings of a pump housing and the openings being connected to an inlet and to an outlet, the gears being received in non-journal-mounted fashion in the openings and the two gears each being equipped with a helical tooth set.
2. Related Prior Art
A gear pump of this kind for homogenizing medical, cosmetic, and technical products and mixtures is known from German Utility Model No. 18 22 807.
It is possible for gears mounted in non-journal-mounted fashion to seal themselves with respect to the housing wall during operation as a result of the differential pressure of the pump.
In German Utility Model No. 18 22 807, coupling of the doubly ball-bearing-mounted drive shaft to the directly drive gear is accomplished by way of an oval stem end that is inserted into an oval bore in the driven gear. This primarily serves the purpose of better emulsification, since the eccentric freedom of movement of the directly driven gear with respect to the drive shaft is one-dimensional and co-rotates. Consistent sealing, over the entire rotation, of the tooth tips in the cylindrical bore in which the gears are received is thereby prevented, since because of its eccentricity, the directly driven gear is lifted to some extent out of its self-sealing position twice during each rotation. To ensure smooth operation, a mounting system for the pump drive shaft that is impact-damped using rubber rings is therefore provided.
A similar bearing system for the driven shaft is known from German Utility Model No. 18 21 554.
A gear pump of this kind for delivering highly aggressive media is known from German Utility Model No. 19 75 041.
It is known from DE 83 31 598 U1 to additionally provide irrigation conduits.
When a pump of this kind is used in the medical field, the actual conveying means, i.e. the gears and the corresponding flow conduits, come into contact with the medical liquids, thus posing the problem of cleaning and disinfection.
The pumps that have become established in the medical field are therefore primarily peristaltic ones, in which the medical liquids are transported by rollers which act externally on flexible tubes.
Although it is possible thereby to ensure that the actual conveying elements do not come into direct contact with the medical liquid, the resulting conveyed flow is nevertheless a pulsating flow, which is not especially suitable, in particular, for applications in hysteroscopy, urology, and arthroscopy.
It is therefore the object of the present invention to create a medical pump which on the one hand is of simple design and also easy to clean, and moreover supplies a continuously variable controllable conveyed flow with high pump efficiency.
SUMMARY OF THE INVENTION
According to the present invention, the object is achieved in that in the case of the gear pump cited initially, the helical tooth set of the gears is configured such that, when viewed along a surface line of the gears, at least two tooth tip/root contact points of the meshing gears are present; and the contour of the tooth spaces of the one gear is matched to the teeth of the other gear in such a way that when a tooth has completely penetrated into the tooth space, its tooth tip almost completely fills up the tooth space radially inside the pitch circle.
The fact that at least two tooth tip/root contact points of the meshing gears are present along a surface line ensures precise concentricity of the meshing gears without wedging forces. The driven gear is in meshing engagement, continuously and in exact alignment, with the undriven non-journal-mounted gear. This eliminates the risk that the undriven gear will come into contact with edges or corners of the overlapping cylindrical housing bores. Coordination of the contours of the tooth spaces and teeth, in such a way that a tooth that has penetrated completely into the tooth space almost completely fills up the latter, on the one hand ensures that only an extremely small cavity volume, i.e. almost no volume at all, is present between the tooth space and tooth and is filled with liquid, and thus only extremely small quantities of liquid can be transported back at all, so that pump output efficiency is maintained at high rotation speeds. If greater quantities were transported back at high rotation speeds, pump output efficiency would be greatly reduced. In addition, this configuration creates outstanding sealing between the delivery and intake sides of the pump.
As a result of the helical tooth set in conjunction with the two-point contact and the particular configuration of the tooth and tooth space, the flow conduit which is necessarily present between the meshing teeth is sealed in such a way that any out-flow through it is efficiently prevented.
It is possible with this special configuration, in the case of meshing gears having a helical tooth set, to dispense with a central journal bearing arrangement for the two gears. The axial bearing points in the conveying chambers which receive the gears are accordingly also omitted. The result is not only to eliminate numerous niches for bacteria, which are difficult to clean and disinfect, but assembly and disassembly are also very simple, since for assembly the gears simply need to be placed into the conveying chamber, with no need to ensure that pivot bearing journals are inserted into a specific bearing point. The special helical tooth set not only results in very quiet-running gears, so that the operator is not disturbed by loud pump noises, but leads to consistently exact meshing engagement with the drive gear. The two gears are received, with a slight radial clearance, in approximately cylindrical overlapping openings. The diameter of the cylindrical openings is thus slightly greater than the diameter of the addendum circle of the respective gears. When the pump according to the invention is then operated with the non-journal-mounted gears, the relative overpressure on the delivery side causes the undriven gear to be displaced somewhat toward the intake side. In other words, during operation, the gears move slightly out of coaxial alignment in the approximately cylindrical chamber in which the respective gear is received. The result of this, when considering the addendum circle of the undriven gear, is an approximately half-sickle-shaped region, widening toward the delivery side, between the addendum circle and the circular inner wall of the conveying chamber in which that gear is received.
This region on the one hand ensures that transfer of the conveyed liquid of a tooth space from the intake pressure state to the outlet pressure is accomplished extremely smoothly, especially in conjunction with the helical tooth set and the configuration of the teeth, resulting not only in extremely quiet conveying but also in a transition from the tooth space to the pressure level with no loss of pressure. The combination of sickle and helical tooth set yields particularly harmonious, smooth, and thus also quiet conveying.
Because of the sickle-shaped region opening toward the delivery side, a force component is created which pushes the undriven gear toward the driven gear. This movement of the meshing gears toward one another results, in combination with the particular configuration of the teeth, in outstanding sealing between these gears, so that a self-sealing effect can be achieved. Backflow from the teeth as they come out of engagement, which impairs pump efficiency, is thereby greatly minimized. This is because the meshing teeth come out of engagement in a direction opposite to the inlet; i.e. quantities of liquid caught between the tooth space and tooth would be conveyed agai
Farner Paul
Hennes Rolf
Kraft-Kivikoski Jürgen
Krattiger Beat
Lampert Hugo Rudolf
Freay Charles G.
St. Onge Steward Johnston & Reens LLC
Storz Endoskop GmbH
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