Rotary expansible chamber devices – Working chamber surface expressed mathematically
Patent
1996-10-21
1998-06-09
Vrablik, John J.
Rotary expansible chamber devices
Working chamber surface expressed mathematically
418171, F04C 210
Patent
active
057624844
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with a Gerotor-type pump which may be used, for example, as an oil pump.
Gerotor-type pumps are well known and comprise an inner rotor provided with external teeth which is located within a hollow outer rotor which is provided internally with teeth meshing with the external teeth of the inner rotor. The outer rotor has one more tooth than the inner rotor and the inner rotor has an axis of rotation which is offset or eccentric with respect to an axis of rotation of the outer rotor. By this arrangement, rotation of one rotor causes the other rotor to rotate as it is driven by the intermeshing teeth. During rotation, due to the eccentricity of the axis of rotation, the intermeshing relationship of the teeth changes progressively forming chambers between the teeth which change in volume to create a pumping action.
The inner rotor of a Gerotor-type pump is designed according to a well-established method. In this method, starting with a circle of diameter A (the base circle), a circle of diameter B (the rolling circle) is rolled around the outside of the base circle while tracing the track of a point at a distance e (the eccentricity) from the centre of the rolling circle. This gives a curve called a trochoid. It is necessary that the rolling circle rolls around the base circle an exact number of times. The ratio of the diameters A to B is the number of "teeth" (n) on the inner rotor.
Next, in designing the inner rotor, a circle of diameter C (the locus or track circle) is moved around the aforementioned trochoid with the centre of the circle on the trochoid. The track of the radially innermost point on the locus circle is the shape of the inner rotor.
Hitherto, the outer rotor of a pump of the Gerotor-type has been designed by drawing a circle of radius R. R is defined by (A+B) divided by 2 plus an adjustment for clearance. Next, n plus 1 centres are defined equally distributed around the circle of radius R. Each of these centres represents the centre of a tooth of the outer rotor. About these centres, circular arcs of radius r are drawn facing towards the centre of the circle of radius R. The radius of the arcs r is defined by C divided by 2 minus an adjustment for clearance. The design of a rotor of conventional type is shown in FIG. 1. In this case, the inner rotor has 5 teeth and the outer rotor has 6 arcuate teeth. As can be seen from FIG. 1, the teeth of the outer rotor are joined by arcs S of a circle, (centred at the centre of the circle of radius R).
The invention provides a pump of the gerotor type comprising an inner rotor and an outer rotor, the inner rotor being located within the outer rotor and being mounted for rotation about a first axis and the outer rotor being mounted for rotation about a second axis which is off-set from said first axis by an eccentricity of the pump, the inner rotor having an outer surface which has a toothed shape and is meshed with an inner surface of the outer rotor which has a toothed shape which has one more tooth than the inner rotor, said toothed shape of the inner rotor being a shape which is generated by moving a first circle around a trochoid with the centre of the circle on the trochoid, characterised in that said toothed shape of the outer rotor has a shape which is generated by moving a second circle around the envelope of the rotated inner rotor trochoid with the centre of the circle on the envelope.
A pump according to the invention operates more smoothly than conventional pumps giving quieter operation and longer life. The pump also has a more efficient pumping action.
Preferably, in a pump according to the invention, said first and second circles have diameters which differ by a predetermined operating clearance between the rotors.
There now follows a detailed description, to be read with reference to the accompanying drawings, of a pump which is illustrative of the invention and of an illustrative method by which shapes of the rotors of the illustrative pump are generated.
In the drawings:
FIG. 1 is a diagrammatic representatio
REFERENCES:
patent: 2965039 (1960-12-01), Morita
patent: 4673342 (1987-06-01), Saegusa
Hill, M.F., Kinematics of Gerotors, The Peter Reilly Co., Philadelphia, PA., 1927, pp. 31-38.
T&N Technology Limited
Vrablik John J.
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