GB2443088A

GB2443088A - Gerotor pump with filling axial rotor slot.

Info

Publication number: GB2443088A
Application number: GB0720434A
Authority: GB
Inventors: Stephen Mark Hodge; Kevin Johanson
Original assignee: CONCENTRIC VFP Ltd
Current assignee: CONCENTRIC VFP Ltd
Priority date: 2006-10-18
Filing date: 2007-10-18
Publication date: 2008-04-23
Anticipated expiration: 2027-10-18
Also published as: GB2443088B; GB0620646D0; GB0720434D0

Abstract

A twin rotor indexing, variable displacement, variable flow gerotor pump has an annulus 14 and two rotors 18, 20 wherein a rotor comprises a peripheral slot 48 extending axially along its outer periphery, preferably symmetrically between adjacent lobes to facilitate filling of the pump chambers in use. The slot may be the full or partial axial length of the rotor and has a width W less than 30 degrees with a depth to width ratio D/W equal to or greater than 1:0.7, preferably 1:3. The slot may be undercut with peripheral width less than the average slot width. The pump may have additional pumped fluid passages 16, 22 in the rotor and annulus.

Description

Pump with Filling Slots The invention relates to pumps suitable for

pumping lubricants and/or coolants for diesel engines. In particular, the invention relates to gerotor pumps having improved filling performance.

It is known from EP0345978 to provide a gerotor pump having an annulus and a rotor, wherein the annulus and/or rotor comprise through passageways to enable greater pressure balance across the pump to help prevent cavitation. The size of the apertures in the rotors and annulus is limited by the structural integrity and performance of the components themselves since to take out too much material from the bodies of these components, would reduce their structural integrity. Moreover, it is known that in order to maintain a smooth movement of the rotors within the annulus, it is necessary for the radius of curvature at the ends of the teeth or lobes on the rotors, as well as the radius of curvature on the recess, or so called minor form diameter, of the rotors to compliment as closely the radius of curvatures of the lobes and recesses in the annulus.

Nevertheless, there is a desire to improve the performance of such gerotor pumps, which can in the circumstances of a split rotor set, act as a variable flow pump, to enable greater filling of the moving pump cavity, which effects transfer of fluid from the inlet to the outlet on rotation of the pump components.

Split rotor variable flow pumps comprise a first rotor rotatable on a fixed axis and a second rotor rotatable on an adjustable axis, which may be indexed relative to the first rotor to vary the output of the pump at a given speed. For example, if the rotors are the same width, when the rotors are coincident, the output is at a maximum, and when the two rotors are indexed at degrees (i.e. opposite) the output is a minimum (zero or near zero) as the effect of the two rotors cancel each other out.

Indexing may cause problems however. If the inlet and outlet of the pump are placed on one side of the rotor set, (e.g. adjacent to the indexing rotor), the indexing rotor can block fluid entry into, and out of, the fixed axis rotor, thus impairing performance. A pump of this type is known as a single end filling variable output pump.

Traditionally, the solution that has been proposed is to provide inlets and outlets on both sides of the rotor set (to form a double end filling variable output pump). This increases the weight, size and complexity of the pump, which is undesirable.

Accordingly, the invention seeks to improve known pumps and rotors. According to one aspect of the invention there is provided a variable flow gerotor pump having an annulus, a first rotor and a second rotor wherein one of the first and second rotors comprises a peripheral slot extending axially along at least part of the periphery of the rotor, to facilitate filling of the pump by a pumped fluid in use..

Advantageously, the slot permits passage of fluid past the rotor nearest to the inlet, and as such allows better filling of fluid to the rotor furthest from the inlet. In the same manner, the slot permits passage of fluid past the rotor nearest to the outlet, and as such allows better ejection of fluid from the rotor furthest from the outlet.

Additionally, the creation of the slots reduces the weight of the pump, and the surface to surface contact between the moving parts thus increasing efficiency.

Other aspects and features of the invention are set out in the claims section later.

Examples of the invention will now be described, by way of example only, with reference to the accompanying drawings in which; Figure 1 is a schematic front elevation view of part of a pump comprising an annulus and split rotor set according to the invention wherein the indexing rotor is indexed through an angle of 120 degrees; Figure 2 is a schematic sectional side elevation view along XX of the pump component shown in figure 1; Figure 3 is an enlarged end view of the pump shown in figures 1 and 2 with emphasis on the shape of the rotors; Figure 4 is an end view of a further embodiment of a rotor according to the invention; and Figure 5 is a schematic view of an undercut slot in a rotor.

Referring to figures 1 to 3 there is shown a pump 10 comprising a casing 12 for holding an annulus 14 having a series of through passages 6. Pump 10 further comprises a pair of rotors 18 and 20 also comprising through passages 22. The pump comprises an inlet port 24 and an outlet port 26. The front rotor 18 is adapted to enable the centre of rotation 30 to be indexed relative to the centre of rotation 28 of the second rotor 20, in a known manner using known indexing mechanisms, thereby to enable variation in the throughput from the inlet to outlet of fluid pumped via pump 10. The centre of rotation of the annulus 14 is shown schematically at point 38 in the front elevation view in figure 3. The point 38 (annulus centre of rotation) is also the point at which the indexing rotor 18 indexes, ie the centre of rotation of part of the indexing mechanism comprising an eccentric, pinion and rack arrangement (not shown).

The pump casing 12 further comprises so called mirror ports 32 opposite the inlet 24 and outlet 26 which mirror ports facilitate filling between the rotors and annulus of pumped fluid in use and pumping out of the fluid. The filling area and output area can be seen as the cross shaded forms 34 shown in figures 1 and 3 respectively. The inlet and outlet port profiles are not shown in figure 3, but these ports provide pressure balancing also.

Rotors 18 and 20 further comprise slots 48 which facilitate in the filling and pumping action of pump 10. Referring in particular to figure 3 it can be seen that the annulus 14 comprises six lobes 40 each being separated by a recess 42. Each of the rotors 18 and 20 comprise five lobes 44 spaced by a recess 46. The lobes of both the rotors and the annulus, are symmetrically spaced. Moreover, the angles of curvature of the ends of the lobes 44 on the rotors are substantially similar to the radius of curvature of the recesses 42 in the annulus, and the radius of curvature of the recesses 46 in the rotors is similar to the radius of curvature of the lobes 40 in the annulus thereby to facilitate movement of the rotors and annulus within the pump. The curvature defining the recess 46 in the rotors is sometimes known as the minor form diameter. The external rotor form and internal annulus form are precisely generated profiles.

In the third form shown in figure 3, slots 48 provide filling slots axially along the circumference of the rotors, that is along the axial length of each of the rotors (see figure 2).

Moreover, the slots 48 are preferably symmetrically disposed between the lobes 44 in the rotors; here centrally located in each of the recesses 46. The slots 48 have a circumferential width W and radial depth D as shown in figure 3. Preferably the width W is smaller than the depth D such that the cross-sectional area of the slot shown in figure 3 has a major axis D rather than W (unlike the exact dimensions shown in figure 3 wherein W is greater than D).

Referring to figure 3, the angle subtended at the mouth of the slot 48 at the recess 46 defined as BB in figure 3 is approximately 200. The angle AA between the ends of the lobes 44 is 72 . Accordingly, in this form the circumferential extent of the mouth of a slot 48 is approximately 28% of the distance between the separation of the lobes 44.

In one form of the invention, the through passages 16 and 22 in the annulus 14 and rotors 18 and 20 are not provided. Accordingly, slots 48 act as both the fluid balancing and filling passages. Such an example is shown in figure 4 wherein a rotor 18' is substantially similar to rotor 18 shown in figure 3 except that the through passages 22 are not provided. Moreover, in this example the slots 48' have a depth D which is greater than the width W. In this example the ratio D:W is 1:0.7. Moreover, the width W is now relatively narrower than the embodiment shown in figure 3 in that the angle BB at the periphery of the rotor 18' is approximately 14 rather than 20 . Beneficially, the narrower slots 48' facilitate better movement of rotor 18' within an annulus 14. Rotor 18' can of course contain through passages 22.

In use the slots 48 and 48' act to enable greater and more efficient filling and output of the pumping fluid without detracting from the smooth movement of the rotors and annulus. In the embodiments shown the rotors extend the entire axial length of the rotor. However, in another form the slots only extend part of the axial length of the rotor. Preferably the slot extends greater than 50% of the axial length of the rotor and more preferably greater than 75% of the axial length. In other forms, only a single rotor, and not a first and second (indexing) rotor, is provided.

Moreover, the shape of the slot need not be U shaped in cross-section or channel-form.

Rather, in one form the slot has a narrower aperture at the rotor periphery than the average width of an axial channel for example formed by undercutting the slot. Beneficially such a slot provides a relatively larger cross-sectional area for fluid flow with a narrower aperture compared to a simple U shape or channel-form slot. As shown in Figure 5 the width to depth ratio W:D can be greater, here about 1:3 for slot 48" in rotor 18". The rotors can be sintered to form the slots and undercut forms.

Claims

1. A variable flow gerotor pump having an annulus, a first rotor and a second rotor wherein one of the first and second rotors comprises a peripheral slot extending axially along at least part of the periphery of the rotor, to facilitate filling of the pump by a pumped fluid in use.

2. A variable flow gerotor pump according to claim 1 wherein the slot is located symmetrically between two lobes of the rotor.

3. A variable flow gerotor pump according any preceding claim comprising two or more slots.

4. A variable flow gerotor pump according to claim 3 wherein a slot is provided between each adjacent pair of lobes of the rotor.

5. A variable flow gerotor pump according to any preceding claim wherein the slot is formed in the periphery of a rotor along the entire axial length of the rotor.

6. A variable flow gerotor pump according to any of claims I to 4 wherein the inlet is formed along only part of the axial length of the rotor; preferably over greater than 50% of the axial length and more preferably more than 75% of the axial length.

7. A variable flow gerotor pump according to any preceding claim wherein the circumferential width of the slot at the rotor periphery is less 30 , more preferably less than 25 and into specific forms 200 and 14 .

8. A variable flow gerotor pump according to any preceding claim wherein the circumferential width of the slot at the periphery is less than the radial depth of the slot in the rotor, preferably wherein the ratio of depth to width is equal or greater than about 1:0.7, and more preferably in the order of 1:3.

9. A variable flow gerotor pump according to any preceding claim wherein the width of slot aperture, at the slot periphery, is less than the average width of the slot, and preferably wherein the slot has an under-cut form.

10. A rotor for a variable flow gerotor pump comprising a peripheral slot extending axially along the outer part of the rotor.

11. A rotor according to claim 10 wherein the slot is located symmetrically between two lobes of the rotor.

12. A rotor according claim 10 or 11 comprising two or more slots.

13. A rotor according to claim 12 wherein a slot is provided between each adjacent pair of lobes of the rotor.

14. A rotor according to any of claims 10 to 13 wherein the slot is formed in the periphery of the rotor along the entire axial length of the rotor.

15. A rotor according to any of claims 10 to 13 wherein the inlet is formed along only part of the axial length of the rotor; preferably over greater than 50% of the axial length and more preferably more than 75% of the axial length.

16. A rotor according to any of claims 10 to 15 wherein the circumferential width of the slot at the rotor periphery is less than 300, more preferably less than 250 and in a specific forms 20 and in another 14 .

17. A rotor according to any preceding claim wherein the circumferential width of the slot at the periphery is less than the radial depth of the slot in the rotor, and preferably wherein the ratio of depth to width is greater than about 1:0.7, and more preferably in the orderofl:3.

18. A rotor according to any of claims 10 to 17 wherein the width of the slot aperture at the slot periphery is less than the average width of the slot, and preferably wherein the slot has an under-cut form.