Rotary expansible chamber devices – Methods
Patent
1995-11-30
1997-07-22
Vrablik, John J.
Rotary expansible chamber devices
Methods
418171, F03C 208, F04C 210
Patent
active
056498152
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a hydraulic machine with an annular gear with internal teeth and, eccentrically mounted in the annular gear, a gearwheel with external teeth which engage with the internal teeth, the internal teeth comprising one more tooth than the external teeth and the contour of one of the sets of teeth being formed by an envelope of a system of generating circles, the midpoints of which lie on a trochoid which, as a rolling circle rolls without slipping on a base circle, can be generated by the movement of a point lying on a radial ray of the rolling circle co-rotating with the rolling circle.
Moreover, the invention relates to a method of producing the contour of a gearwheel or annular gear of such a hydraulic machine, in which a trochoid is generated using a rolling circle rolling without slipping on a base circle and a point lying on a radial ray of the rolling circle co-rotating with the rolling circle.
A machine of that kind and a method of that kind are known from U.S. Pat. No. 2,421,463. In machines of that kind, the radius of the base circle is an integral multiple of the radius of the rolling circle, the multiplication factor corresponding to the number of teeth of the gearwheel. According to Dubbel, "Taschenbuch fur Maschinenbau", 13th edition, volume 1, Berlin, Heidelberg, New York 1970, page 144, the trochoid described can also be generated other than by rolling two pairs of circles.
Machines of the known kind have proved useful as pumps or as motors in many instances of application. However, there are always problems with the internal seal and with the formation of Hertzian stresses. The internal seal is impaired by leaks, as a consequence of which the hydraulic fluid is able to escape at the sealing points between internal teeth and external teeth from areas of relatively high pressure to areas of lower pressure. Hertzian stresses affect the "lubricity" and thus the wear and tear on the machine.
The invention is based on the problem of producing a hydraulic machine having a relatively large displacement and a method of creating the contour of a gearwheel of such a machine.
This problem is solved in a hydraulic machine of the kind mentioned in the introduction in that the spacing of the point from the midpoint of the rolling circle is larger than the radius of the rolling circle.
For the sake of simplicity, the following explanations relate to the formation of the contour of a gearwheel. A corresponding procedure is used to form the contour of an annular gear.
The displacement of the machine is closely allied to the magnitude of eccentricity, that is to say, the spacing of the point from the midpoint of the rolling circle, so that a small eccentricity corresponds to a relatively small displacement. Previously, the rolling circle radius had been regarded as the upper limit for the magnitude of the eccentricity, inter alia because the trochoid forms loops, that is, crosses over itself along its circumference when the eccentricity becomes larger. This also leads to the system of circles being superimposed on themselves. Despite this, it produces an envelope or generating curve of an envelope, which defines the form of the gearwheel. The gearwheel has in that case relatively deep tooth spaces with relatively sharp-edged teeth projecting steeply between the spaces. Such a gearwheel contour surprisingly provides a good engagement factor, and consequently a good seal between adjacent chambers, which are pressurized with a pressure difference and which are defined by the co-operation of internal teeth and external teeth, and low Hertzian stresses.
It is also preferred for the ratio of the spacing of the point from the midpoint to the radius of the rolling circle to lie in the range from 1.25 to 1.6 and for the ratio of the radius of the generating circles to the radius of the rolling circle to lie in the range from 1.8 to 2.2. Excellent meshing ratios are achieved with these ratios.
Preferably, the midpoints of the generating circles of the system are arranged side by side in a circumfere
REFERENCES:
patent: 4518332 (1985-05-01), Saegusa
patent: 4657492 (1987-04-01), Saegusa
patent: 4673342 (1987-06-01), Saegusa
Hansen Gunnar Lysh.o slashed.j
Petersen Hans Christian
Danfoss A/S
Vrablik John J.
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