Rotary expansible chamber devices – Trapped fluid relief
Patent
1982-09-07
1985-10-22
Vrablik, John J.
Rotary expansible chamber devices
Trapped fluid relief
418201, F04C 216
Patent
active
045485623
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a hydraulic pump. More particularly it relates to positive displacement hydraulic pumps wherein the pumping elements comprise intermeshing, external, helical gears.
BACKGROUND ART
This invention is an improvement in positive displacement pumps having intermeshing gears. Various kinds of positive displacement pumps are known in the fluid machinery art including vane pumps wherein a pump rotor rotates in a pumping cavity and carries on its periphery pumping vanes, slipper pumps, having loosely mounted slippers carried by a pump rotor in a pumping cavity, and internal-external gear pumps wherein one pumping element is an external gear and the companion meshing gear element is an internal gear. My invention comprises a positive displacement pump which, unlike the previously described positive displacement pump, comprises two external gears that mesh in their respective pump cavities. Examples of such external gear pumps are shown, for example, in U.S. Pat. No. 2,746,394 (Dolza et al); U.S. Pat. No. 2,996,999 (Trautman); and U.S. Pat. No. 2,871,794 (Mosbacher).
In a gear pump of the kind shown in the above-idenified prior art patents, the cavities between the external gear teeth and the surrounding pump housing act as fluid pumping chambers as they carry fluid from an inlet port to an outlet port upon rotation of the gears. As in the case of most gearing systems, the helical gear teeth of my improved pump have a contact ratio for the gears that is greater than unity. Thus there is an overlap in the gear tooth engagement pattern as one pair of meshing teeth begins to engage prior to disengagement of the preceding pair of meshing gear teeth. This creates in the space between the meshing gear teeth a volume of fluid which at one instant decreases in volume and at another instant increases in volume. The instant at which the volume changes from a compression mode to an expanding mode corresponds to the instant that the line of action for the meshing gears intersects the line connecting the centers of rotation of the gears.
In order to avoid a hydraulic lock that would reduce pumping efficiency and create pump noise as well as undesirable hydraulic pressure forces in the pump, it is common practice to use an end plate an each axial side of the meshing pump gears and to provide a recess in the end plates to permit discharge of the fluid trapped in the gear tooth space thus providing communication between that space and the adjacent port. This provides a pressure relief that prevents a buildup of pressure in the trapped fluid in the tooth space of the meshing gear teeth.
The improvements of my invention make it possible to eliminate the need for using ported end plates in a gear pump assembly of this kind. This involves a strategic port design so that each tooth space volume between two meshing teeth in a helical gear pump having a form contact ratio greater than unity registers with the cutoff edge of the outlet cavity at one axial end of the tooth at the same instant the opposite end of the same tooth space volume registers with the inlet edge of the inlet port. Thus there is no opportunity for a pressure pulsation to occur in the fluid trapped between two meshing gear teeth. The use of ported plates with pressure recesses at the ends of the pump gears is not required. The assembly thus is simplified, its cost reduced and the space required for a given pump capacity is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of a gear pump showing the meshing pump gears, the inlet port and the outlet port.
FIG. 2 is a view of the plane of contact of the gear teeth of FIG. 1 as seen from the perspective of section line II--II of FIG. 1.
FIG. 3 is a sketch showing the gear geometry of one of the pump gears of FIG. 1.
FIG. 4 is a diagram showing the geometry of two meshing gears for a gear pump assembly such as that shown in FIG. 1.
FIG. 5 is an enlargement of a portion of the meshing gears for the gear pump assembly of FIG. 1 showing a volum
REFERENCES:
patent: 2159744 (1939-05-01), Maglott
patent: 2193671 (1940-03-01), Dolza
patent: 2462924 (1949-03-01), Ungar
patent: 2746394 (1956-05-01), Dolza et al.
patent: 2871794 (1959-02-01), Mosbacher
patent: 2996999 (1961-08-01), Trautman
patent: 4193749 (1980-03-01), Yamazaki et al.
patent: 4210410 (1980-07-01), Ohtani
patent: 4290739 (1981-09-01), Korse
patent: 4371324 (1983-02-01), Gustafsson
Ford Motor Company
Harrington Donald J.
Vrablik John J.
Zerschling Keith L.
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