Rotary expansible chamber devices – With changeable working chamber magnitude – Intermeshing rotary members
Reexamination Certificate
1999-10-13
2001-09-04
Vrablik, John J. (Department: 3748)
Rotary expansible chamber devices
With changeable working chamber magnitude
Intermeshing rotary members
Reexamination Certificate
active
06283735
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a variable-delivery external gear pump comprising a casing, at least one rotatively driven pair of gears comprising two intermeshing spur gears which form with shell surface areas of the casing and axial sealing surface areas a delivery space comprising a low-pressure side connected to a pump inlet port and a high-pressure side connected to a pump outlet port, and a piston, serving to rotatively mount one spur gear of said pair of gears, the piston being shifted relative to the other spur gear of said pair of gears so as to vary the delivery of said pump together with the one spur gear by charging said high-pressure side with fluid against the force of a return element. More particularly, the invention concerns an external gear pump which automatically regulates itself with increasing speed.
2. Description of Related Art
One external gear pump in the field concerned is known from German Patent DE 41 21 074 A1.
SUMMARY OF THE INVENTION
It is on the basis of this prior art that an object of the invention is to provide a variable-delivery external gear pump which pumps a fluid to be delivered as consistently and pulsation-free as possible.
This object is achieved in that formed in at least one axial sealing surface area adjoining a sealing land of the sealing surface area is at least one pocket connecting a zone of deepest tooth engagement of the spur gears to either the pump outlet port or the pump inlet port.
The invention is based on an external gear pump comprising, in a casing, a rotatively driven pair of gears with two intermeshing spur gears. The pair of gears is enclosed by casing surface areas which together with axial sealing surface areas contacted by the faces of the spur gears define a delivery space comprising a low-pressure side connected to a pump inlet port and a high-pressure side connected to a pump outlet port. To define the volumetric displacement of the pump, one of the spur gears is rotatively mounted on a piston which, together with this spur gear, is mounted in the casing shiftable relative to the other spur gear. Preferably, the piston is linearly shiftable parallel to the axis of rotation of the spur gear mounted on the piston. By shifting the one spur gear relative to the other spur gear, the intermeshing length of the spur gears is varied for the preferred axial shift.
The intermeshing length is automatically reduced with increasing pumping pressure which increases/decreases depending on the pump speed. Varying the delivery or automatically adjusting the pump to increasing pumping pressure is achieved by charging the piston with fluid at the high-pressure side. The compressive force of the high-pressure fluid is counteracted by the force of a return element. The return element is formed preferably by a compression spring. The compressed fluid forces the piston in the direction of a reduction in the intermeshing length and the return element opposes this compressive force.
Preferably, the pump finds application as a lube pump, more particularly for engine oil delivery in reciprocating piston engines.
In accordance with the invention, a pocket or kidney-shaped recess is formed in at least one axial sealing surface area bordering a sealing land of this sealing surface area and connecting a zone of deepest tooth engagement of the gear teeth with either the pump outlet port or the pump inlet port. The axial sealing surface area directly adjoins a face of one of the spur gears. The sealing land of the sealing surface area covers the bottom of the tooth gap of the deepest tooth engagement of the two gears. The pocket connects the tooth gap in the zone of deepest tooth engagement to the next tooth gap at the high-pressure side or low-pressure side.
Opposite one sealing surface area without pocket, a lesser resistance discharge of the high-pressure fluid from the tooth gap of deepest tooth engagement is assured. The invention thus creates an external gear pump, in which the fluid of the high-pressure side is used to automatically limit the delivery while, however, eliminating or at least reducing the squeezed oil effects involved in such external gear pumps having the known single-plane axial sealing surface areas.
Preferably, the depth of the pocket is, at most, a 5th or, at least, a 20th of the maximum intermeshing length of the two gears, this also applying to any further pocket formed. When further pockets are formed, the depth of each may be the same. If a pocket is formed at both the high-pressure side and the low-pressure side of the sealing surface area, the pocket at the low-pressure side preferably has a depth less than that of the pocket at the high-pressure side. In one preferred embodiment, the otherwise single-plane axial sealing surface area is stepped down to the again single-plane pocket of constant depth. The maximum intermeshing length exists at least at zero delivery and in accordance with the reset characteristic of the return element in the lower speed range of the pump.
The pocket takes up a surface area of minimally 5% and maximally 20% of the surface area covered by the spur gear when in rotation, as measured at the upper edge of the pocket. With increasing pocket surface area, the friction between the sealing surface area and the sweeping face of the spur gear becomes advantageously less.
The pocket is preferably provided at the high-pressure side of the axial sealing surface area, since, in this case, the displacement of fluid in the delivery direction from the squeeze zone of the tightest tooth engagement is facilitated. However, the pocket can also be provided at the low-pressure side, since, in this case, the amount of fluid in the entrapment zone is reduced in any case.
Preferably, a pocket is incorporated into the axial sealing surface area at both the low-pressure side and high-pressure side adjoining the sealing land. Also preferred is that further axial sealing surface areas for the spur gears are each provided with a pocket at the high-pressure side, and even more preferably, each provided with a pocket at the low-pressure side of the respective sealing surface area.
The pump may also comprise several pairs of gears. In particular, a single spur gear, which is then preferably driven, may intermesh with one or several other spur gears and, in this way, form several pair of gears of the pump. Preferably, at least one pocket of the aforementioned kind is also formed in the same way in the zone of deepest tooth engagement of this additional pair of gears or in each additional pair of gears. In one preferred embodiment of the invention, one such additional spur gear is also shiftable relative to the common spur gear for regulating pump delivery by pressurization. In this arrangement, the delivery characteristics of the pair of gears may be the same as each other or differ from each other.
REFERENCES:
patent: 1458204 (1923-06-01), Tibbetts
patent: 2149326 (1939-03-01), Wilkin
patent: 2354992 (1944-08-01), Gottlieb
patent: 3669577 (1972-06-01), Swanson
patent: 4233005 (1980-11-01), Bottoms et al.
patent: 4740142 (1988-04-01), Rohs et al.
patent: 698 627 (1940-11-01), None
patent: 29 01 179 (1979-07-01), None
patent: 35 28 651 (1987-02-01), None
patent: 41 21 074 (1993-01-01), None
patent: 781697 (1957-08-01), None
patent: 46-2624 (1971-01-01), None
patent: 57-73880 (1982-05-01), None
Schreiber Bernd
Stutzle Gunther
Ratner & Prestia
Schwabische Huttenwerke GmbH
Vrablik John J.
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