GB2187233A - Rotary positive displacement pump - Google Patents

Abstract

An N, N+1 type pump is mountable in a recess about the forward end of a driven shaft of an internal combustion engine via a housing member 15 having a flange 20 which is adapted to be clamped against a face of the engine cylinder block by a cover 21. The cover has recesses forming a radial inlet passage (26, Fig. 2, not shown) a kidney-shaped inlet port (28), a kidney- shaped outlet port (27) and a radial outlet passage 25. A seal 35 is formed at each circumferential side of each of radial passages 25 (26), between the cover and the radially outwardly facing surface of flange 20. <IMAGE>

Description

SPECIFICATION Improvements relating to rotary positive displace ment pump assemblies This invention relates to rotary positive displace ment pump assemblies such as N(N+1) pump assemblies and has a particularly useful but not exclusive application in relation to internal combus tion engineswherea sourceof pressurefluid is required, for example for lubrication purposes and/or for supply to servo mechanisms.

According to the invention in one aspectthere is provided a pump assemblyforan internal combustion engine, comprising an annular inner rotor having N lobes evenly spaced along its outer periphery, an annularouterrotorhaving N+1 lobes evenly spaced along itsinnerperiphery,thelobesofthe innerand outer rotors being in mesh to provide pumping chambers and the rotors being eccentrically disposed relative to each other, a housing member having therein a recess which provides a bearing forthe outer rotor and which has a radially outwardly projecting peripheral flange adapted to be clamped against a face ofthe cylinder block ofthe engine, and a cover adapted to be secured to said face of the cylinder block about said housing member and to clamp said flange against said face of the cylinder block, said cover defining an inlet port and an outlet port opening to said pumping chambers and two recesses opening to said ports respectively and to the face of the cover which faces the cylinder block, at least one of which recesses extends radially outward beyond said flange, and means forming a seal between the coverandthe radially outwardly facing surface of said flange at a location attach circumferential side of said one recess.

In one preferred construction according to the invention, the cover is moulded from a plastics material and the seal forming meansateachofsaid locations comprises one or more axially extending ribs which are formed integrally with the cover and which form an interference fit with the radially outwardly facing surface of the flange. Preferably the cover is formed with hollow bosses which are disposed for abutment with said face ofthe cylinder block at opposite sides respectively of each of said inlet and outlet apertures and the ribs are formed at the inner sides of said bosses, and which are adapted to receive clamping bolts or otherfasteners for securing the cover to the cylinder block.

According to a preferred feature ofthe invention, a surface position ofthe cover at a location radially inward ofthe inlet port is in closely axially facing relationship with an axially-facing surface of the inner rotor and has formed therein a groove extending over the circumferential length ofthe inlet port and radially inward of the inlet port, which groove is connected to be supplied with pressure fluid by the pump.

In another aspect, the invention provides a rotary positive-displacement pump comprising a rotary pumping means and a casing enclosing the rotary pumping means and providing surfaces in closely axially facing relationship with the pumping means, one of said surfaces having formed therin an inlet port through which fluid passes into the pumping means and thenceto an outletofthe pump, said onesurface having formed therein a groove disposed radially inwardly of the inlet port and extending over substantially only the circumferential length of the inlet port, said groove being connected to be supplied with pressure fluid by the pumping means.

One embodiment ofthe invention will now be described by way of example. The description makes reference to the accompanying drawings in which: Figure 1 is an axial section, on the line 1-1 of Figure 2, of a pump according to the invention, and Figure 2 is an end view ofthe pump in the direction of the arrow 2 of Figure 1.

Referring to the drawings, the pump is ofthe N(N+1)typeand incorporates accordingly an annular inner rotor 10 having N lobes evenly spaced about is outer periphery and an annular outer rotor 11 having N+1 lobes evenly spaced about its inner periphery and in mesh with the lobes ofthe inner rotor. The forward end portion of a shaft 12 of an internal combustion engine extends through the central bore ofthe inner rotor. The shaft has two flats 13 on its external surface and the bore of the inner rotor is of complementary shape, whereby a rotary drive can be transmitted to the inner rotor by the shaft.The outer rotor is mounted eccentrically relative to the inner motor in a housing member l5which is secured in an annular recess inthefrontface 16ofthe cylinder block 17 oftheengineandwhich also provides an axial abutment for one end of the inner rotor. To reduce the weight of the housing member, parts of its radially outer surface are cut away leaving radially extending ribs 18 projecting into engagement with the outer wall ofthe recess for locating purposes. The housing member has one axial end portion 19 projecting outside the recess and formed with an outwardly projecting flange 20which abuts the front face 16 of the block.

A cover member 21 moulded from a strong plastics material is secured to the front face of the engine block overthe rotors 10,11 and housing member 15 by fixing bolts 22. The cover member is in the form of a shell open at its rearward side and is shaped to provide a sealing flange 23 along its outer edge and a central hollow boss 24which extends abouttheshaft 12 and which abuts the inner rotor 10. The cover member also provides two radially-extending recesses 25,26 opening attheirradially-innerendsinto respective kidneyshaped ports 27,28 extending about the axis ofthe shaft and communicating with the pumping chambers formed by the rotors 10,11. Attheir radially outer ends these recesses open axially to an inlet duct (not shown) and a delivery duct 30 formed in the engine block 17.

A preformed sealing gasket 32 is located in rebates and grooves which extend continuously along the inner edge of the flange and across hollow bosses 33 for the sealing bolts. The bosses abut the face ofthe cylinder blocK At circumferentially opposite sides of each ofthe two recesses, where the bosses 33 extend up to thegoutwardlyfacing surface ofthe flange 20, the surfaces ofthe bosses which contact the flange are formed with axially extending ribs 35 which form a tightfitwith the flange 20 and form seals preventing fluid from leaking round between the recesses forthe fluid along the outer circumferences of the flange and thus preventing leakage of hi ~ h pressure fluid from the delivery passage to the inlet passage and the ingress of air into the inlet passage.Thus as the cover member is drawn bythe fixing bolts up to the front face ofthe cylinder blockthe ribs 35 are forced into contact with the flange and become resiliently deformed, producing a tight seal. The proximity ofthe sealing ribs to the fixing bolts 22 minimises the possibility of deformation ofthe cover shell form tending to prevent the axial ends ofthe ribs from being pressed into tight engagement with thefrontface of the cylinder block.

A groove 36 is formed in the axial face ofthe central boss ofthe cover memberadjacentthe inner rotor and extends in an arcto locations justbeyondthetwo circumferential ends ofthe inlet port at a position radially between the inlet port and the central aperture fortheshaft 13.

One end ofthe groove 36 is connected to the leading end ofthe outlet port so that pressure fluid is supplied to the groove. This fluid prevents air from being drawn through the annular clearance between the shaft and the periphery ofthe central aperture through the boss 24 and thence radially outward through the axial working clearance between the cover member and the pumping means into the fluid flowing through the inlet port28 into the pumping means by the low pressure ofthisfuid.

Since the maximum suction which can be created at the inlet port 28 is equal to the ambient atmospheric pressure, it is only necessary forth fluid in the groove to be at a pressure slightly in excess of atmospheric pressure to prevent the induction of air, and in an alternative arrangement a short separate additional outlet port is provided adjacentthe leading end of the main outlet port 28 for the sole purpose of supplying fluid under low pressure to the groove 36.

Claims (6)

1. A pum p assem blyfor an internal combustion engine, comprising an annular inner rotor having N lobes evenly spaced along its outer periphery, an annular outer rotor having N+ 1 lobes evenly spaced along its inner periphery, the lobes ofthe inner and outer rotors being in mesh to provide pumping chambers and the rotors being eccentrically disposed relative to each other, a housing member having therein a recess which provides a bearing for the outer rotor and which has a radially outwards projecting peripheral flange adapted to be clamped against a face ofthe cylinder block ofthe engine, and a cover adapted to be secured to said face of the cylinder block about said housing member and to clamp said flange against saidface of the cylinder block, said cover defining an inlet port and an outlet port opening to said pumping chambers andtwo recesses opening to said ports respectively and to the face of the cover which faces the cylinder block, at least one of which recesses extends radially outward beyond said flange, and meansformingaseal between the coverand the radially outwardly facing surface of said flange at a location at each circumferential side of said one recess.

2. A pump assembly as claimed in Claim 1, wherein the cover is moulded from a plastics material and the seal forming means at each of said locations comprises one or more axially extending ribs which are formed integrally with the cover and which form an interference fitwith the radiallyoutwardlyfacing surface ofthe flange.

3. A pump assembly as claimed in claim 2, wherein the cover is formed with hollow bosses which are disposed for abutment with said face of the cylinder block at opposite sides respectively of each of said inlet and outlet apertures and the ribs areformed atthe inner sides of said bosses, and which are adapted to receive clamping bolts or other fasteners for securing the cover to the cylinder block.

4. A pump assembly as claimed in anyone of claims 1 to 3, wherein the recess which opens to the oulet port opens at its end remote from the outlet port to the face ofthe coverwhich is to adjoin the cylinder block thereby to deliver pumped fluid to a passage in the cylinder block.

5. A rotary positive-displacement pump comprising a rotary pumping means and a casing enclosing the rotary pumping means and providing surfaces in closely axially facing relationship with the pumping means, one of said surfaces having formed therein an inlet portthrough which fluid passes into the pumping means andthenceto an ouletofthe pump, said one surface having formed therein a groove disposed radially inwardly of the inlet port and extending over substantially only the circumferential length ofthe inlet port, said groove being connected to be supplied with pressure fluid by the pumping means.

6. A pump assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.