GB2443089A

GB2443089A - Split rotor variable output gerotor pump

Info

Publication number: GB2443089A
Application number: GB0720439A
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: GB0720439D0; GB2443089B; GB0620648D0

Abstract

A gerotor pump having an annulus 34 and a split rotor set comprising first 18 and second 20 rotors and an indexing mechanism 27, 28 that may include a piston, rack and pinion (50, 52, 30 Fig. 7) enabling eccentric movement of the second rotor so as to vary the performance of the pump. The pump is configured to operate with a reduced output range e.g. less than a zero to 100% flow range that would otherwise be achievable for a rotor set of the combined axial length RASL of equal first and second rotors. To achieve this, the indexing rotor has a length IRAL shorter than that FRAL of the non-indexing rotor so that when the rotors are in antiphase (i.e. 180{ out of phase) there is a net output. Alternatively there may be a limitation applied to the indexing mechanism to limit second rotor displacement or indexing range between 30 and 150 degrees.

Description

Improvements in Gerotor Pump Performance The invention relates to

gerotor pumps for use for example as coolant or lubricant pumps for engines and in particular a gerotor pump adapted to enable a variable output.

It is known to provide a gerotor pump having a split rotor set wherein the rotors are engaged in a single annulus, one of the rotors having a fixed rotational axis relative to the annulus and the second rotor having a rotational axis which is moveable relative the axis of rotation of the annulus. In earlier systems, the axial length of the first and second rotors is equal such that when the axis of rotation of the first and second rotor are aligned (zero phase shift) there is a perceived maximum output from the pump. When the axis of rotation of the second rotor is indexed 180 , it pumps completely out of phase with the first rotor and the effect of both the first and second rotors is to cancel each other out and there is zero flow from the pump.

The performance characteristics of a pump are determined by several properties, one of which is the axial length of the rotor set which helps define the maximum volume of fluid which can be pumped. All other properties being equal the maximum output range achievable by a gerotor pump is the 100% and 0% output range achievable with a 50:50 split ratio in the first and second rotors. Zero flow is only achievable for a rotor set having a 50:50 split ratio (ie where the first and second rotors are of equal length) and the first and second rotors are 180 out of phase.

The inlet and outlet ports of gerotor pumps are "timed" to prevent the pumping cavities being simultaneously in fluid communication with both said inlet and outlet. The port timing is therefore designed to prevent a loss in volumetric efficiency of the pump at a set index angle.

It is perceived that indexing one of the rotors leads to a drop in the volumetric efficiency as the port timing is not optimum for that position of rotor.

Gerotor pumps are positive displacement pumps and as such the output available generally varies linearly with speed. However, known pumps actually experience a drop in responsiveness close to the 0 degree and 180 degree indexation positions. By responsiveness we mean that the pump output is less sensitive to changes in index angle near these points. A higher degree of change in output is generally seen for index angles away from 0 and 180 degrees (i.e. the gradient of a index angle vs. output graph is steeper).

The invention seeks to provide improvements in variable flow performance of such pumps by providing improved responsiveness and ability to control fluid flow from a pump.

According to one aspect of the invention there is provided a gerotor pump having an annulus and a split rotor set comprising a first and second rotor, and an indexing mechanism enabling movement of the second rotor so as to vary the performance of the pump, wherein the pump is configured to operate with a reduced output range effected by predetermining the extent of indexation of the second rotor relative to the first rotor to provide a minimum indexation angle between the first and second rotors of greater than 0 degrees.

The applicant has discovered that instead of a drop in volumetric efficiency when the second rotor is indexed (due to port timing), the volumetric efficiency remains the same or increases.

Therefore the subject pump can be run at a minimum index angle (greater than Zero) which is both high output (due to the efficiency increase) and close to the responsive region of pump performance (i.e. away from 0 degrees offset).

Also, as the amount of pre-indexation is generally small (less than 20 degrees), the pump priming is not adversely affected.

The reduced output range is achieved by pre-determining the extent of indexation which the second, indexing, rotor can achieve in use. Preferably, the indexing mechanism is configured to provide a minimum indexation angle, or pre-indexation angle, between the first and second rotors of greater than 5 . Preferably the minimum indexation angle is controlled to be less than 30 and more preferably in the range of 15 to 25 and in a particular form equal to approximately 20 . Additionally, preferably the maximum indexation angle between the first and second rotors is limited to less than 180 and more preferably to less than 175 . It is possible to ensure that the maximum indexation angle is not limited below a certain angle such as 150 Preferably, the maximum indexation angle is set to between 150 and 175 , more preferably 155 to 165 and in a particular preferred form, substantially equal to about 160 .

In addition, a reduced output range is supplemented by having a fixed ratio of axial lengths of the first and second rotors of less than 1 to I or 50:50. Preferably, the axial length of the second rotor is greater than approximately 20% of the axial length of the rotor set. More preferably, the length of the second rotor is in the range of 25 to 45% of the combined axial length of the rotor set. In preferred forms the axial length of the second rotor is approximately 30% and more preferably approximately 40% of the axial length of the rotor set.

Embodiments 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 sectional side elevation of part of a pump according to the invention, Figure 2 provides a schematic end elevation of the relative position of the first and second IS rotors with respect to the annulus at different angles of indexation, Figure 3 is a schematic cross section side elevation view of a second embodiment of a pump according to the invention, Figure 4 provides different end views of the first and second rotor and annulus from the pump shown in figure 3 at different angles of indexation, Figure 5 is an enlarged view of the relative positions of the first and second rotor relative to their respective rotational axes for a slightly modified rotor compared to figures 1 and 3, Figure 6 is an enlarged schematic view of the relative positions of the centres of rotation of the first and second rotor relative to the annulus in Figure 5, Figure 7 is a schematic view of an indexing mechanism forming part of the pump shown in figures 1 and 3, and Figure 8 provides schematic end views of different pinions according to the invention.

Referring to figure 1 there is shown a pump 10 according to the invention comprising a drive gear 12 mounted on a drive shaft 14 having a rotational axis 16. Pump 10 further comprises a split rotor set comprising a first rotor 18 and a second rotor 20. The first rotor 18 is mounted on a shaft 22 being co-axial with drive shaft 14 and fixed relative thereto. The second rotor 20 is mounted on an eccentric 26 via bush 24. Eccentric 26 comprises an off-centre indexing shaft 27 the centre of which is coincidental with annulus centre 35. Pinion 30 is mounted on the indexing shaft 27. Together the eccentric 26, indexing shaft 27 and pinion 30 form part of an indexing mechanism 32 which co-operates with a rack and suitable feedback mechanism to enable movement of the centre 28 of the second or indexing rotor 20.

Axis 28 of the eccentric is coincidental with the axis of the non-indexing rotor when there is no pre-indexing evident (full 100% output position). Axis 35 of the eccentric is, and remains coincidental with the annulus axis, and it is about this axis 35 that the indexing rotor indexes.

The dimensional offset of axis 28 to axis 35 of the eccentric 26 represent the offset of the particular rotor set used. The eccentric 26 is located, and rotates in, pump housing 36.

Pinion 30 locates on, and is fast with, the eccentric. Together the eccentric 26 and pinion 30 form part of an indexing mechanism.

Pump 10 further comprises an annulus 34 which is housed in a pump body comprising first and second casings 36 and 38. Casing 38 defines a fluid inlet 40 and outlet 42.

As can be seen in figure 1 whilst the axial length of the rotor set RSAL, being the combined axial length of the first rotor FRAL and second rotor IRAL, is equal to the axial length of the annulus 34. The first and second rotors 18, 20 do not have equal axial lengths. In this embodiment, the ratio of first to second rotor axial lengths is 3 to 2 or 60% to 40% of the rotor set axial length RSAL. The output range achievable from the pump shown in figure us 100% when the first and second rotors 18, 20 are fully aligned (0 out of phase) and 20% when the second rotor 20 is indexed to be 180 out of phase with the first rotor 18.

Accordingly, the output range for pump 10 is 100% to 20% of that of the 100% to 0% output range of a gerotor pump having a 50:50 split in the axial length of the first and second rotors.

The output range can be limited further using specific configurations within the indexing mechanism as described later.

Referring to figure 2, an end elevation (looking from the pinion side) is shown of the split rotors 18, 20 and annulus 34 In figure 2A, the first and second rotors 18 and 20 are fully aligned and a full output is achievable from the pump. In figure 2B the second rotor 20 is indexed 90 out of phase with the first rotor 18 and only 60% output is achieved.

In figure 2C, the second rotor 20 is indexed 1800 out of phase with the first rotor 18 and accordingly only a 20% flow is achievable.

Referring to figure 3, there is shown a pump 10' substantially similar to the pump 10 shown tO in figure 3, and therefore having like components labelled with the same reference number, except that the relative axial lengths of the first and second rotors, 44 and 46, are different to that shown in figure 1. In this example, the ratio of the lengths is 7 to 3, or 70% of the total rotor set axial length (equal to the axial length of the annulus 34)is provided by the first rotor 44 and 30% by the second, indexing, rotor 46.

In this embodiment, the output range is variable between a maximum when the first and second rotors 44, 46 are aligned as shown in figure 4A, and 40% of this maximum when the second rotor 46 is indexed 180 out of phase with the first rotor 44, as shown in figures 4C.

In figure 4B, the second rotor 46 is indexed 90 out of phase with the first rotor 44 and this achieves a 70% output compared to the maximum shown in figure 4A.

Referring to figure 5, there is shown in greater detail, the relative positions of the centres of rotation of the components forming the moving parts of the pump but for a slightly different rotor set 18', 20' and annulus 34'. The annulus 34' can be seen to rotate about a fixed centre (being restrained by casing 36), at annulus centre 35. The first (fixed or non-indexing) rotor 18' rotates about a fixed rotational centre on axis 16 which is offset from the annulus centre in a known manner. The second, indexing rotor, 20' rotates about a further axis of rotation 28 which here is shown to be indexed 20 out of phase with the fixed rotor centre 16.

The relative positions of the centres is shown in even greater detail in figure 6.

It will be noted in figure 5 that the rotors 18' and 20' each comprise four teeth spaced 90 apart, and forming therefore a symmetrical shape about the centre of rotation of each of the rotors. In contrast, the annulus 34' comprises 5 lobes each adapted to receive the teeth of the rotors as they rotate within the gerotor pump. Accordingly, the lobes in the annulus are spaced 72 apart and are symmetrically spaced around the centre of rotation of the annulus.

Beneficially, the configuration allows for very shallow lobes which enable ease of rotation of the rotor within the annulus and moreover provide a large pumping capacity.

Referring to figure 7 there is shown further detail of the indexing mechanism 32 enabling relative movement of the axes of rotation of the indexing rotor (20 in figure 1 and 46 in figure 3) relative to the first rotor (18 in figure 1 and 44 in figure 3).

Indexing mechanism 32 comprises a rack 48 mounted on a piston 50 which can form part of a feedback mechanism linked to the fluid communication loop being served by pump 10 or 10'. Accordingly, piston 50 can be adapted automatically to drive rack 48 thereby to rotate pinion 30 and effect indexation of the indexing rotor 20, 46 as appropriate.

As shown in figure 7, the rack 48 has a length LI comprising teeth 52 for engaging the teeth of pinion 30. Here the length LI can be configured relative to the circumference of pinion so as to provide limited rotation of the pinion between pre-set angles. Moreover, as shown in figure 8, the extent of indexation of the pinion 30 can be limited by the circumferential length of teeth provided by the pinion. As shown in figure 8, in one embodiment a pinion 30a has teeth over slightly greater than 180 of its circumferential length whereas pinion 30b has teeth over approximately 155 of a potential circumferential length. Accordingly, through the co-operation of the length Li of teeth 52 on rack 48 and the circumferential length of the teeth on pinion 30, it is possible to pre-determine the extent of indexation of the second indexing rotor 20 or 46 forming part of pump 10 or 10'. Moreover, by configuring the indexing mechanism 32 such that the indexing rotor is offset from the fixed rotor by a pre-determined indexation angle greater than 0 , it is further possible to limit the maximum output range of the pump within specified limits. However, in a preferred form, the length LI of the rack 48 and the circumferential length of the pinion 30 is designed so as not to limit in themselves, the indexation of the second rotor 20. Rather, in a preferred form the design of the piston 50 and co-operating cylinder C in which the piston 50 reciprocates in use, are designed so as to effect a limitation in the extent of movement of the rack 48 and hence pinion 30 and subsequently indexation rotor 20.

Beneficially, the provision of reduced indexing, pre-indexing, and variation in the ratio of the lengths of the first and second rotors, enables considerable control over the output range of a gerotor pump, moreover, considerable savings can be achieved in reduction of the use of materials for example in the pinion 30 which does not have teeth over a 3600 circumference.

Additionally, the length of the rack 48 and piston 50 assembly is considerably reduced since piston having length L2 is reduced compared to prior art designs and of course length Li is reduced as described above, thereby providing material savings in manufacture.

The extent of indexation of the indexing rotor can firstly be fixed as a minimum value, or pre-indexed value, whereby the second rotor (20, 20', 46') is preset to a minimum offset of say 500 or 20 relative to the first rotor (18, 18', 44) and then the extent of indexation can also be limited by the use of the indexing mechanism 32 and in particular through the use of piston 50. This is achieved using an indexation mechanism which does not allow 360 of movement of the indexing rotor and preferably the limits are determined by a piston arrangement with limited reciprocating movement which define the end points, including the pre-index angle, of the indexing rotor.

IS

Claims

1. A gerotor pump having an annulus and a split rotor set comprising a first and second rotor, and an indexing mechanism enabling movement of the second rotor so as to vary the performance of the pump, wherein the pump is configured to operate with a reduced output range effected by predetermining the extent of indexation of the second rotor relative to the first rotor to provide a minimum indexation angle between the first and second rotors of greater than 0 degrees.

2. A gerotor pump according to claim 1 wherein the indexing mechanism is configured to provide a minimum indexation angle between the first and second rotors of greater than about 5 degrees.

3. A gerotor pump according to claim 2 wherein the indexing mechanism is configured to provide a minimum indexation angle between the first and second rotors which is less than 300 and more preferably in the range of about 15 degrees to about 25 degrees.

4. A gerotor pump according to claim 3 wherein the minimum indexation angle is substantially equal to about 20 degrees.

5. A gerotor pump according to any preceding claim wherein the maximum indexation angle between the first and second rotors is limited to less than about 180 degrees and more preferably to less than about 175 degrees.

6. A gerotor pump according to claim 11 wherein the maximum indexation angle between the first and second rotors is not less than about 150 degrees.

7. A gerotor pump according to claim 12 wherein the maximum indexation angle is between abotu 150 degrees and about 175 degrees, and more preferably in the range of about degrees to about 165 degrees.

8. A gerotor pump according to claim 13 wherein the maximum indexation angle is substantially equal to 160 degrees.

9. A gerotor pump according to any preceding claim wherein the axial length of the second rotor is less than the axial length of the first rotor.

10. A gerotor pump according to claim 9 wherein the axial length of the second rotor is greater than approximately 20% of the axial length of the rotor set axial length.

11. A gerotor pump according to claim 10 wherein the axial length of the indexing rotor is in the range of 25% to 40% of the rotor set.

12. A gerotor pump according to claim 11 wherein the axial length of the indexing rotor is approximately 30% of the axial length of the rotor set.

13. A gerotor pump according to any of claims 9 to 11 wherein the axial length of the indexing rotor is approximately 40% of the axial length of the rotor set.

14. A gerotor pump having an annulus and a split rotor set comprising a first and second rotor, and an indexing mechanism enabling movement of the second rotor so as to vary the performance of the pump, wherein the pump is configured to operate with an output range less than a 100% flow range (0 to maximum flow) achievable for a rotor set of the combined axial length of the first and second rotors.