Toothing system for a gerotor pump, and method for geometric determination thereof

Abstract

A toothing for a gerotor pump comprises a plurality of outer teeth (10) at a gerotor inner element (1) and a plurality of inner teeth (20) greater by one at a gerotor outer element (2), wherein a centre (M1) of the gerotor inner element (1) is offset from a centre (M2) of the gerotor outer element (2) by an eccentricity (e), the outer teeth (10) thereby meshing with the inner teeth (20). A contour of the outer teeth (10) at the gerotor inner element (1) is essentially defined by a curve of a single ellipse from a tooth tip (11) continuously via tooth flanks (13) to a transition radius (14) towards a tooth space or a tooth root (12); wherein the principal axis of the ellipse is arranged radially to the gerotor inner element (1) and the centre of the ellipse determines a radius (R.sub.min) at the gerotor inner element (1) which corresponds to the maximum meshing depth of the gerotor outer element (2) between the outer teeth (10) at the meshing.

Claims

1. A toothing for a gerotor pump comprising: a plurality of outer teeth at a gerotor inner element; and a plurality of inner teeth greater by one at a gerotor outer element, wherein a center of the gerotor inner element is offset from a center of the gerotor outer element by an eccentricity such that the outer teeth thereby mesh with the inner teeth, and wherein a contour of the outer teeth at the gerotor inner element is defined by a curve of a single ellipse from a tooth tip continuously via tooth flanks to a transition radius towards a tooth space or a tooth root, and further wherein a principal axis of the ellipse is arranged radially to the gerotor inner element and ellipse determines a radius at the gerotor inner element which corresponds to a maximum meshing depth of the gerotor outer elements between the outer teeth during the meshing, and wherein, in rotation of the gerotor outer element, a root clearance is defined at an apex between two of the outer teeth by the radius of the maximum meshing depth and the eccentricity.

2. The toothing for a gerotor pump according to claim 1, wherein the contour of the outer teeth extends radially and is defined by the eccentricity multiplied by a factor of 4.

3. The toothing for a gerotor pump according to claim 1, wherein the principal axis of the ellipse is defined by the eccentricity multiplied by a factor of 4.

4. The toothing for a gerotor pump according to claim 1, wherein minor axis of the ellipse is orthogonal to the principal axis and is defined by the eccentricity multiplied by a factor between 0.5 to 2.5.

5. The toothing for a gerotor pump according to claim 1, wherein a contour of the gerotor inner element is respectively formed in a concave shape between two outer teeth.

6. The toothing for a gerotor pump according to claim 1, wherein a contour of the gerotor inner element is respectively formed in a concave shape between two outer teeth, and wherein the concave contour includes the root clearance defined by the radius of the maximum engagement of the gerotor outer element, the maximum engagement of the gerotor outer element defined by an extent of the eccentricity multiplied by a factor between 0.1 and 0.15.

7. The toothing for a gerotor pump according to claim 1, wherein a contour of the inner teeth of the gerotor outer element results from an intersection of an envelope of a family of curves which is set along a course of movement of the gerotor pump through the contour of the outer teeth of the gerotor inner element.

8. The toothing for a gerotor pump according to claim 1, wherein the gerotor inner element comprises a number of at least five outer teeth.

9. The toothing for a gerotor pump according to claim 1, wherein the gerotor outer element is rotably supported in the gerotor pump and is rotably dragged along via the meshing by a rotary drive motion of the gerotor inner element.

10. The toothing for gerotor pump according to claim 1, wherein the gerotor pump is adapted to convey lubrication oil to a combustion machine.

11. The toothing for gerotor pump according to claim 1, wherein the gerotor pump is adapted to convey transmission oil.

12. The toothing for gerotor pump according to claim 1, wherein the gerotor pump is adapted to convey hydraulic oil.

13. A method for geometric determination of a toothing for a gerotor pump which comprises a plurality of outer teeth at a gerotor inner element and a plurality of inner teeth greater by one at a gerotor outer element, wherein a center of the gerotor inner element is offset from a center of the gerotor outer element by an eccentricity such that the outer teeth thereby mesh with the inner teeth, the method comprising: setting one single ellipse, a principal axis of which is arranged radially to the gerotor inner element as well as setting a dispersed radial arrangement of such ellipses according to the plurality of outer teeth; defining contour sections of the outer teeth along a curve of each ellipse; defining contour sections between the outer teeth along a radius that is determined by a center of each ellipse, wherein the radius at the gerotor inner element is corresponding to a maximum meshing depth of the gerotor outer element between the outer teeth at the meshing; defining, in rotation of the gerotor outer element, a root clearance, at an apex between two of the outer teeth, by the radius of the maximum meshing depth and the eccentricity; and defining transition radii which connect the contour sections of the outer teeth with the contour sections between the outer teeth.

14. The method for the geometrical determination of a toothing for a gerotor pump according to claim 13, further comprising: setting a radial extension of the elliptical contour of the plurality of outer teeth as a function of the eccentricity.

15. The method for the geometrical determination of a toothing for a gerotor pump according to claim 13, further comprising: setting a dimension of the principal axis of the ellipse as a function of the eccentricity.

16. The method for the geometrical determination of a toothing for a gerotor pump according to claim 13, further comprising: setting a dimension of an orthogonal minor axis of the ellipse as a function of the eccentricity.

17. The method for the geometrical determination of a toothing for a gerotor pump according to claim 13, further comprising: defining concave recesses in the contour sections between the outer teeth and determining a recess depth to the radius that is determined by a center of the ellipse as a function of the eccentricity.

18. The method for the geometrical determination of a toothing for a gerotor pump according to claim 13, further comprising: defining a contour of the inner teeth of the gerotor outer element via an intersection of an ellipse curve which is defined by the contour of the outer teeth of the gerotor inner element.

Description

(1) The invention will be explained in detail hereinafter with the aid of an exemplified embodiment and with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a gerotor inner element with outer teeth of a toothing for gerotor pumps according to one embodiment of the invention, indicating to dimension ratios;

(3) FIG. 2 shows meshing between the gerotor inner element and a gerotor outer element of a toothing for gerotor pumps according to one embodiment of the invention, indicating dimension ratios;

(4) FIGS. 3A-3H show a sequence of a course of movement, rotating to the left, of a toothing for gerotor pumps according to the embodiment of the invention.

(5) The gerotor comprises a gerotor inner element 1 and a gerotor outer element 2. The gerotor is arranged in a pump chamber of a gerotor pump, not shown. The gerotor inner element 1 is engaged with a rectangular profile of a driven pump shaft 3 and drags along the gerotor outer element 2 via meshing. The gerotor outer element 2 is received in a cylindrical circumferential wall of the pump chamber, not shown, so as to be supported in a sliding manner and to be rotatable via the outer circumference.

(6) When the gerotor rotates to the left, the outer teeth 10 move into and out of the inner teeth 20 as meshing occurs. In a rotational angle section which lies, in the direction of rotation, upstream of the bottom dead centre of the meshing on an axis of the eccentric offset, displacement of a medium being conveyed, in particular an oil, occurs, said medium being drawn in on the other hand in a rotational angle section which lies, in the direction of rotation, downstream of the bottom dead centre. Ejection of the displaced oil and drawing-in occurs in a known manner through an outlet, not shown, and an inlet of the gerotor pump which each issue into the pump chamber on the face-side via a kidney-shaped opening upstream or downstream of the bottom dead centre respectively.

(7) FIG. 1 shows an embodiment of the gerotor inner element 1 with the outer teeth 10 which have an elliptical contour form the tooth tip 11 to beyond the tooth flanks 13, which contour ends only at a transition radius 14 to the tooth roots 12. An ellipse is shown at an outer tooth 10 pointing downwards, the ellipse curve thereof defining the contour of the tooth tip 11 and the tooth flanks 13. In accordance with the provided method for the geometric determination of the gerotor toothing, the essential dimension ratios are given in dependence upon an eccentricity e of the gerotor, i.e. an extent of the offset between a centre M.sub.1 of the gerotor inner element 1 and a centre M.sub.2 of a gerotor outer element 2.

(8) An ellipse, which is used as an auxiliary curve for the geometric determination of the contour of the outer teeth 10, has a principle axis which is arranged radially to the centre M.sub.1 of the gerotor inner element 1. The length of the principle axis is longer than the extent of the eccentricity e by a factor of proportionality. In the illustrated embodiment, this factor of proportionality is preferably set to the value of 4, but it can also deviate therefrom by a few decimal places. The minor axis of the ellipse has a length which is longer than the extent of the eccentricity e by a factor of proportionality a. In the illustrated embodiment, the factor of proportionality a is set to the value of 1.5, but it can also have another value within a range of 0.5 to 2.5, preferably between 1.0 and 2.0. The factor of proportionality a, which defines the length of the minor axis of the ellipse in dependence upon eccentricity, influences the width of the outer teeth 10 in the circumferential direction of the gerotor inner element 1.

(9) The centre of the ellipse, where the principle axis and minor axis intersect, determines a radial extent of the gerotor inner element 1 up to which a tip circle of the inner toothing of the gerotor outer element 2 enters between the outer teeth 10 to a maximum extent as meshing occurs, and thus sets a minimum radius R.sub.min up to which a tooth root or tooth space of the outer toothing of the gerotor inner element 1 at least must be recessed. Since the radius R.sub.min is set by the centre of the ellipses and the factor of proportionality of the principle axis of the ellipse in the illustrated embodiment has the value of 4, the radial length of an outer tooth 10 corresponds to the factor 2 of the eccentricity, i.e. the radius of a tip circle of the outer tooth is greater than the radius R.sub.min by the factor 2 of the eccentricity e and the radius of a pitch circle or roll circle of the gerotor is greater than the radius R.sub.min by the extent of the eccentricity e.

(10) As shown in FIGS. 1 and 2, each tooth space between the outer teeth 10 has a slightly concave recess which is connected to the transition radii 14 to form the tooth flanks 13. An apex of the slightly concave recess is, in the circumferential direction of the gerotor inner element 1, in the centre of each tooth space and at the same time forms the tooth root 12. At the tooth root 12, the contour of the gerotor inner element 1 has, in relation to the radius R.sub.min, a recess depth, the radial extent of which corresponds to a factor of proportionality b to the eccentricity e. In the illustrated embodiment, the factor of proportionality b has a value of 0.125, but it can also have another value in a preferred range of 0.10 to 0.15.

(11) The radial extent of the recess depth can likewise be referred to as a root clearance 15 which indicates a clearance of distance in the case of maximum meshing between the tooth root 12 of the gerotor inner element 1 and the elevation of the tooth space between the inner teeth 20 of the gerotor outer element 2 at the bottom dead centre of meshing. The root clearance influences the size of a root space having the shape of the concave recess and increases a flow diameter for allowing the oil to escape between the outer teeth 10.

(12) With reference to FIGS. 3A to 3H, the rolling behaviour of a gerotor rotating to the left, i.e. a cyclical relative movement between the gerotor inner element 1 and the gerotor outer element 2, will be described hereinafter. The illustrations show, not necessarily one after the other, different functionally explained rotational angle positions of the gerotor. When the gerotor rotates to the left or anti-clockwise, torque is transmitted from the gerotor inner element 1 to the gerotor outer element 2 and the medium being conveyed, or oil, is displaced from the inner teeth 20 through the outer teeth 10.

(13) In FIG. 3A, the left outer tooth 10 begins to come into contact with the inner tooth 20 in a very flat contact angle. In FIG. 3B, the outer tooth 10 continues to slide into the inner tooth 20 at a very flat contact angle. Owing to the flat contact angle, a slight Hertzian loading is produced between the tooth flank 13 of the outer tooth 10 and the opposite contour of the inner tooth 20. In FIG. 3C, the right outer tooth 10, which enters the inner tooth 20, effects displacement work, whereby the oil in the inner tooth 20 is urged upwards and to the left through a curved wedge gap along the left tooth flank 13 of the outer tooth 10. In FIG. 3D, the right outer tooth 10 has completely entered the inner tooth 20, whereupon a wedge gap is produced along the tooth flanks 13 on both sides of the outer tooth 10 to the compression side and to the suction side.

(14) With a rotary movement component, there is superposition of a pivoting movement between the outer tooth 10 and inner tooth 20 about the bottom dead centre of the meshing owing to the eccentricity. The pivoting movement progresses from the right-hand side in FIG. 3C, via a centre position at the bottom dead centre in FIG. 3D, to the left-hand side in FIG. 3E. The wedge gap is further reduced on the side of the left tooth flank 13 of the right outer tooth 10 whilst a following outer tooth 10 moves on the left towards the contact with an inner tooth 20. In FIG. 3F, the right outer tooth 10 begins to slide out of the inner tooth 20 whilst the left outer tooth 10 comes into contact with the following inner tooth 20, in a comparable manner to FIG. 3A, and begins to slide therein, whereby displacement begins again.

(15) FIG. 3G shows a rotational angle position in which two adjacent outer teeth 10 each transfer torque to the gerotor outer element 2 by their flank contact with the inner teeth 20. FIG. 3H shows once again the very flat contact angle when the outer teeth 10 move into or out of the inner teeth 20, whereby very small Hertzian stresses occur in the region of the contact surfaces of the toothing.

(16) As shown in FIGS. 3A to 3H, the contact surfaces produced along the tooth flanks 13 can be represented by relatively large substitute radii. The relatively large substitute radii produce an increase in the surface contact occurring along the toothing contour compared with conventional tooth geometries. In a manner comparable with a design condition for sliding bearings, the wear on the frictional pair is minimised by the large substitute radii and the flat contact angles.

(17) Hydrostatic effects at the sliding gap of the surface contact can be assumed, not least owing to the additional displacement flows along the contact surfaces which ensure a dynamic lubricating film for wetting the toothing contour. Within the anticipated operating parameters, the hydrostatic effects theoretically prevent direct surface contact on the tooth flanks 13. The theoretical assumption coincides with experimental practice to the extent that according to test series by the inventors, no measurable or visible wear occurred on the gerotor toothing in accordance with the invention.

(18) As an alternative to the illustrated embodiment with the threshold tooth number 5/6 as the ratio of outer teeth 10 of the gerotor inner element 1 to inner teeth 20 of the gerotor outer element 2, the gerotor can likewise be designed with a corresponding tooth number of 6/7, 7/8 or 8/9, wherein the effect of some of the described advantages of the tooth geometry in accordance with the invention is further increased.

LIST OF REFERENCE SIGNS

(19) 1 Gerotor inner element 2 Gerotor outer element 3 Pump shaft 10 Outer tooth 11 Tooth tip 12 Tooth root 13 Tooth flank 14 Transition radius 20 Inner tooth a Factor of proportionality of the ellipses—minor axis b Factor of proportionality of a root clearance e Eccentricity M.sub.1 Centre of gerotor inner element M.sub.2 Centre of gerotor outer element R.sub.f Root circle of the gerotor inner element R.sub.min Radius of the engagement depth of meshing