Pump having a main outlet communicating with a secondary outlet by a gap

GROUND OF THE INVENTION

The invention relates to pumps and more particularly, but not exclusively, to pumps of the type comprising an externally toothed or lobed inner rotor mounted eccentrically within and meshing with an internally toothed or lobed rotor. One pump of this type comprises a lobed inner rotor which rotates eccentrically within an outer rotor having one more lobe than the inner rotor, the inner and outer rotors making permanent sliding contact at points spaced around their periphery and defining sealed spaces which decrease in volume between fixed inlet and outlet ports.

Pumps of this type are often used as oil pumps in internal combustion engines. The pump rotors are generally mounted in a housing, part of which may be constituted by a pocket in the engine block, and a driving shaft projects into the housing to drive the inner rotor which in turn drives the outer rotor.

BRIEF SUMMARY OF THE INVENTION

According to the present invention there is provided a pump comprising a housing, pumping elements mounted within the housing for pumping fluid from an inlet to a main outlet. The main outlet communicates with a secondary outlet by way of a control gap which filters the fluid passing into the secondary outlet.

In preferred arrangements, the housing comprises a body portion and a cover plate. The body portion is formed so as to define the inlet and outlets and provides a wall to define with the outer rotor, the control gap between the main and secondary outlets.

It is a preferred feature that the secondary outlet has an orifice through which filtered fluid can flow. Ideally the orifice is connected to external tubing to direct the filtered fluid to predetermined locations.

In certain embodiments, the pumping elements comprise an externally toothed or lobed inner rotor mounted eccentrically within and meshing with an internally toothed or lobed outer rotor which is mounted for rotation within and relative to the housing. Conveniently, the inner rotor is adapted to be driven in rotation, the rotation causing rotation of the outer rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings in which:

FIG. 1

is a plan view of an interior of a housing body of a pump, according to the present invention, with rotors inserted;

FIG. 2

is a section on line II—II of the housing body of

FIG. 1

with rotors inserted and a cover plate attached;

FIG. 3

is a side view of an interior of a housing body of an alternative pump according to the present invention;

FIG. 4

is a plan view of an interior of a housing body of an alternative pump according to the present invention;

FIG. 5

is an enlarged view of part of

FIG. 4

;

FIG. 6

is a plan view of another alternative pump according to the present invention;

FIG. 7

is a cross-section on line VII—VII of

FIG. 6

;

FIG. 8

is a plan view of an interior of a housing body of a further alternative pump according to the present invention;

FIG. 9

is a cross-section on line IX—IX of

FIG. 8

with a cover plate attached;

FIG. 10

is a plan view of an interior of a housing body of a still further pump according to the present invention; and

FIG. 11

is a cross-section on line XI—XI of

FIG. 10

with a cover plate attached.

DETAILED DESCRIPTION OF THE INVENTION

In

FIGS. 1 and 2

there is shown a pump

10

comprising a housing having a main body

11

and a cover plate

12

. The main body

11

is formed so as to provide a pocket for receiving an inner rotor

13

and an outer rotor

14

. The housing also provides a fluid inlet

17

and a main outlet

18

. The inner rotor

13

is, in use, driven about its central axis A by a drive shaft (not shown) which projects through the cover plate

12

. The inner rotor

13

has external lobes

15

and the outer rotor

14

has internal lobes

16

, there being one more lobe

16

than lobes

15

. The rotation of the inner rotor

13

causes the outer rotor

14

to rotate about its central axis B, the rotors being eccentrically mounted relative to each other. The lobes

15

,

16

make sliding contact and a pumping action is effected by the decreasing volume of the sealed spaces between the inner and outer rotors from the inlet

17

to the main outlet

18

. The general operating principal of this type of pump is known.

In pump

10

, the main body

11

of the housing provides a wall

20

which defines one edge of the main outlet

18

. Radially outwards of the wall

20

is a secondary outlet

21

. Fluid pumped from the inlet

17

to the main outlet

18

is able to pass into the secondary outlet through a control gap

22

between the end of the wall

20

and the outer rotor

14

. The control gap

22

is of a predetermined size (this is exaggerated in the drawings for the sake of clarity) so as to provide a filtering action for fluid passing into the secondary outlet. Clearly the size of the gap

22

is chosen so as to provide a desired filtering action.

The secondary outlet

21

has an orifice

23

to which a tube

24

or tubes are connected to direct the filtered fluid to a chosen location. In alternative arrangements the filtered fluid may be directed to oil galleries which may be internal or external to the pump or may be sprayed directly from the orifice

23

to a required location.

The pump

10

is suited to use in an internal combustion engine to pump lubricating oil from the inlet

17

to the main outlet

18

. Oil from the main outlet

18

can be used for some lubrication purposes, but filtered oil entering the secondary outlet

21

can be used for specific lubrication purposes where it is important not to have large foreign bodies in the oil.

In one particular example, favorable results have been obtained with a control gap

22

of 175 &mgr;m±50 &mgr;m. However, it should be stressed that this is merely an example of one suitable arrangement and other sized gaps can be used depending on the filtering effect required. Also, the radial length of the secondary outlet can be varied.

FIG. 3

shows a more complicated housing main body

30

for a pump

10

. Many features are the same as for the embodiment shown in

FIGS. 1 and 2

and so have been given the same reference numerals. There are some differences to the precise form of the inlet

17

and main outlet

18

. In addition the orifice

23

leading from the secondary outlet

21

extends generally axially relative to the rotors

13

,

14

, rather than generally radially, as in the first embodiment.

In

FIGS. 4 and 5

there is shown an alternative pump

30

in which many features are similar to the pump

10

in

FIGS. 1 and 2

. Like parts have, therefore, been given like reference numerals. In

FIGS. 4 and 5

, however, the wall

20

has been omitted and the secondary outlet

31

is formed as a recess in the wall of the housing main body

11

radially outwards of the outside diameter of the outer rotor

14

. The recess

31

communicates with the outlet

18

by a control gap

32

formed in the housing main body

11

. The control gap

32

is again of a predetermined radial width to provide a filtering action and can be the normal clearance between the outer rotor

14

and the main body

11

of the housing.

In

FIGS. 6 and 7

there is shown another embodiment of a pump

40

. Again, features in common with pump

10

shown in

FIGS. 1 and 2

have been given the same reference numbers. In

FIGS. 6 and 7

, the inlet

17

and the outlet

18

are provided in the main body

11

of the housing and also in the cover plate

12

. The outlet

18

in the cover plate

12

extends partially over the top axial face of the outer rotor

14

and communicates by way of a control gap

41

with the secondary outlet

21

. This secondary outlet

21

in the cover plate

12

may be suitable for spraying filtered fluid directly onto a chain or gear, for example, or may have an optional spray jet component

42

coupled to it, as shown in broken lines in FIG.

7

.

In

FIGS. 8 and 9

, again parts similar to those in

FIGS. 1 and 2

have been given the same reference numbers. A pump

50

in

FIGS. 8 and 9

has a secondary outlet

51

in the form of a tube

52

which extends through the main body

11

of the housing and through the outlet so as to communicate at its radially inner end with a bearing surface

53

for an axially extending spigot portion

54

of the inner rotor

13

. Fluid passes from the lower outlet

18

through the bearing clearance and into the radially inner end of the tube

52

.

It will be appreciated that the control gap described above may sometimes be the actual clearances between two existing components, but sometimes these clearances may need to be enlarged to ensure that there is sufficient flow.

In the configurations shown, a number of the configurations show oil being drawn directly through a clearance, whilst others require a step to be introduced to achieve the desired clearance locally, where the available clearance is insufficient to establish a reasonable flow. The requirement for a local step depends on the clearance between components in a particular pump design. In the majority of pump designs, it should be possible to draw a flow of oil through the rotor bearing clearances. A local step would normally, but not always, be required when drawing oil through axial clearances (as these are generally smaller). However, some pump designs, perhaps in high pressure applications, may require a local step to draw oil from radial clearances.

In

FIGS. 10 and 11

, there is shown a further embodiment of pump

60

and again parts similar to those in

FIGS. 8 and 9

have been given the same reference numerals. A circumferential groove

61

is formed in the radially outer bearing surface of the spigot portion

54

of the inner rotor

13

. A secondary outlet in the form of a bore

62

through the main body

11

of the housing is provided, the bore

62

opening at its inner end in the bearing surface

53

opposite the groove

61

. An alternative bore position

63

is also shown in FIG.

10

.

In this arrangement, fluid passing through the inner rotor bearing clearance is drawn into the groove

61

. The fluid is then free to pass around the inner rotor to be drawn off along the bore

62

which constitutes the secondary outlet.

Two bore examples are shown, but others are possible. This variation could be achieved in certain configurations on the inner or outer rotor, on either axial or radial faces. A filter step may be required to achieve the required flow rate of fluid and filtering effect, although in some cases this step feature may not be required (as shown in

FIGS. 10 and 11

) where the available clearances are suitable for both purposes.

Although the control gap for filtering outlet fluid has been described above in connection with n (n+1) type pumps, it will be appreciated that the same principle could be used in the outlet regions of other types of pumps, such as vane or roller type pumps, and internal and external gear pumps.