GB2088480A - Centrifugal pumps - Google Patents

Abstract

The centrifugal pump (55) comprises a support element (11, 12) provided with a flange portion (11) arranged to seal a pump casing (50) in a fluid-tight manner, and a rotating shaft (4) to the ends of which are fixed am impeller (2) and a rotary motion transmission member (3). Between the shaft (4) and support element there are mounted two rows of ball bearings (28) and a plurality of seal assemblies including a seal (8), to provide a seal between the shaft (4) and the support element. The seal assembly (8) comprises a gasket (25) urged by resilient means against a rear surface of the impeller (2). The pump may be a vehicle water pump. <IMAGE>

Description

SPECIFICATION Integral pumping unit for centrifugal pumps This invention relates to an integral pumping unit for the impeller of centrifugal pumps, particularly for water pumps mounted on motor vehicles.

In motor vehicle water pumps there is known to exist the problem of supporting the centrifugal pump impeller in an effective and economical manner, using only small overall dimensions.

One design at present used by many rolling bearing manufacturers consists of constructing and selling support assemblies constituted by a transmission shaft arranged to receive at its respective ends the pump impeller and a pulley for transmitting motion from the motor to the shaft, and by a bearing of special type comprising two rows of rolling bodies but without the inner race, which is replaced by sliding tracks for the rolling bodies provided directly in said shaft. The two rows of rolling bodies are suitably spaced apart in order to provide the shaft with two support points sufficiently far apart to ensure rotational stability.

The described assembly is mounted in a suitably machined housing provided in the cover of the pump casing, and fixed therein by a setscrew, the end stem of which engages in a bore suitably provided in the outer race of the bearing. The described assembly can also be fixed in said housing by other suitable means, for example by forcing.

The rolling bodies are protected from contact with water by two water-tight shields fixed by light forcing into seats provided in the inner surface of the outer race of the bearing, so as to seal the annular chamber lying between the outer race of the bearing and the transmission shaft.

In addition, a seal assembly is housed between the bearing and impeller in a seat provided in the inner surface of said housing, comprising a socket bearing containing an annular cylindrical sintered graphite gasket urged by a spring, with predetermined pressure, against a front surface of the impeller hub, in order to form a seal against it.

The described design is not free from drawbacks.

In particular, the fixing of the bearing in the pump cover housing can involve assembly and machining problems (shaft not centred, bores not aligned etc.) which when high thermal and mechanical stresses are present can lead to poor operation due to residual gaps, with considerable damage to the motor. This is possible because the machining and assembly of parts which have to be precisely coupled together, and which is carried out in successive stages by different firms (pump manufacturer, bearing and shaft manufacturer, seal assembly manufacturer) leads to inevitable inaccuracies. In addition, the assembly must be carried out by particularly expert operators. Finally, such a design leads to a relatively large overall axial dimension and low seal efficiency.

The object of the present invention is to provide an integral pumping unitforcentrifugal pumps free from the described drawbacks, and in particular of small overall axial size.

Said object is attained according to the present invention by an integral pumping unit for centrifugal pumps, particularly for motor vehicle water pumps, arranged for mounting on a pump casing of said centrifugal pumps, characterised by comprising a transmission shaft rotating about its axis and provided at its two ends with a centrifugal impeller and a member for transmitting rotary motion to said shaft respectively, a support element for said shaft provided at one end with a flange portion arranged to seal said pump casing in a fluid-tight manner and facing said impeller, two rows of rolling bodies disposed between said shaft and said support element to make the former rotatable relative to the latter with low friction, and a plurality of seal assemblies arranged to provide a water-tight seal between said shaft and said support element, said transmission shaft comprising an outer surface on which said rolling bodies directly roll, and said seal assemblies comprising at least one gasket disposed between said impeller and said rolling bodies and urged by resilient means against a rear surface of said impeller in order to provide a seal between this latter and a socket housed in said support element, and in which said gasket is contained.

The present invention will be more apparent from the description of some embodiments thereof given hereinafter by way of non-limiting example, with reference to the accompanying drawings in which: Figure 1 is an axial section through an integral pumping unit representing a first embodiment of the present invention; Figure 2 is an axial section through an integral pumping unit representing another embodiment of the invention of Figure 1; Figure 3 shows an identical detail of the pumping units of Figures 1 and 2 to an enlarged scale; Figure 4 is an axial section through a centrifugal water pump for motor vehicles in which the integral unit of Figure 1 is mounted; and Figure 5 is a further embodiment of the pumping unit of Figure 1.

With reference to Figure 1, the reference numeral 1 indicates an integral pumping unit comprising a centrifugal impeller 2, a toothed pulley 3, a shaft 4 rotating about its axis and having said impeller 2 and pulley 3 forced respectively on to its ends 5 and 6, a support element 7 and a seal assembly 8.

The support element 7 comprises a flange portion 11 and a sleeve portion 12 perpendicular to the portion 11, and is traversed parallel to the sleeve 12 by a cavity 13 of cylindrical symmetry. The cavity 13 is constituted-by a shallow recess 14 provided in a front face 15 of the flange 11, from which there extends a frusto-conical compartment 16 with its major diameter facing the surface 15, and by a cylindrical seat 17 provided in the sleeve 12 and divided from the frusto-conical compartment 16 by a shoulder projection 18. The shallow recess 14, the compartment 16 and the seat 17 are coaxial to each other and to the shaft 6, and succeed each other in the described order.

Immediately afterthe shallow recess 14 in the frusto-conical compartment 16, there is provided a seat 21 housing a cylindrical socket 22 of metal or other material of suitable strength, forming part of the seal assembly 8 of known type. This comprises said socket 22, and an annular gasket 25 of L section housed in the socket 22 in such a manner as to slide inside it as a piston, under the thrust of a spiral spring. The socket 22 and gasket 25 are bored, and are mounted with slight slack on the hub 20 of the impeller 2.

-A metal ring can be disposed between the gasket 25 and relative spring in orderto protect this latter The gasket 25 and its spring are retained in the socket 22 by an annular stop 26 provided on the socket 22. The gasket 25 is urged by the spring against a rear surface 19 of the impeller 2, facing the surface 15, and exerts a predetermined axial pressure thereon. In this way a sliding seal is formed between the surface 19 and gasket 25 in order to protect the cavity 13 from water infiltration.

A cylindrical ring 27 is forced into the cylindrical seat 17 and rests on the shoulder 18. Between the ring 27 and shaft4there are disposed rolling bodies constituted by two rows of balls 28 which roll in a first pair of hemispherical tracks 31 provided in the shaft 4 between its ends 5 and 6, and in a second pair of hemispherical tracks 32 provided in an inner surface of the ring 27. The ring 27, shaft 4 and rolling bodies 28 constitute a support assembly 10 for the impeller 2. The ring 27 is locked axially both bythe shoulder 18 and by a screw 34 housed in a threaded bore 35 provided in the sleeve 12 parallel to the flange 11.

In the surface 33 of the ring 27 there are provided seats 36, into which water-tight shields 38 are lightly forced, these comprising annular lips 37 arranged to slide with predetermined pressure on a surface 41 of the ends 5 and 6 ofthe shaft 4, in orderto exert a sliding seal thereon to isoiate the rolling bodies within an annular chamber 42 lying between the shaft4and ring 27.

The frusto-conical compartment 16 communicates with the outside through a bore 43 provided with predetermined inclination in the support element 7 between the flange portion 11 and the hub portion 12. A slinger ring 44 comprising a rim 45 flared with the same inclination as the bore 43 is keyed on to the hub 20. In an embodiment not shown, the slinger ring 44 can be replaced by a drip-breaking groove suitably provided in the hub 20.

The flange portion 11 oftheelement7alsopos- sesses a peripherally outer portion 46 of smaller thickness in which bores 47 are disposed along a circumference arranged to be connected in a fluidtight manner, by virtue of an annular surface 48, to a pump casing 50 (Figure 4) in order to seal this latter.

Figure 2 shows an integral unit 1 similarto that of Figure 1. In particular, the shaft 4, the impeller 2, the pulley 3 and the seal assembly 8 are identical. The support element 7 is however slightly different in that it is composed of a flange portion 11 identical to that of Figure 1 and a ring portion 27 rigid with the flange portion 11. The hemispherical tracks 32 in which the balls 28 rotate are provided in an inner surface 33 of the ring portion 27. Seats 36 are also provided in the same surface 33 for housing watertight shields 38 completely similar to those of Figure 1 in order to isolate the rolling bodies 28 within the annularchamber42 lying between the ring portion 27 and shaft 4.A frusto-conical compartment 16 similar to that of Figure 1 is provided in the element 7, and houses the seal assembly 8 by means of a seat 21. The compartment 16 communicates with the outside through a bore 43 provided with predeter mined inclination in the element 7 between the flange portion 11 and ring portion 27. A slinger ring 44 similar to that of Figure 1 is mounted on the hub 20 ofthe impeller 2.

Figure 3 is a detailed view to an enlarged scale of the connection between the shaft 4 and ring or ring portion 27. The already described details are visible, in particular the hemispherical tracks 31 and 32 in which the balls 28 roll with their axes of symmetry 49 perpendicular to the shaft 4.

The profile of each hemispherical track 31 is sym metrical about an axis 51, and likewise the profile of each hemispherical track 32 is symmetrical about an axis 52. The axes 51 of the profiles of the first pair of hemispherical tracks 31 are perpendicular to the axis of the shaft4 and are spaced apart by a predetermined distance A. The axes 52 of the profiles of the second pair of hemispherical tracks 31 are perpendicularto the axis ofthe ring 27, which is coaxial to the shaft 4, and are spaced apart by a predetermined distance B greater than A. The hemispherical tracks 34 are therefore offset from the tracks 32. Because of the different axial position of the pairs of tracks 31 and 32, the balls 28 become arranged between each track 31 and each track 32 in such a manner that their axes 49 lie between the axes 51 and 52 of each track.

In this manner, the balls 28 are not in contact with the entire surface of the tracks 31 and 32, but only with a part thereof.

More specifically, the balls 28 roll on surfaces 53 pertaining to the tracks 32 and on surfaces 54 pertaining to the tracks 31. The surfaces 53 are constituted by the adjacent halves ofthe tracks 32, while the surfaces 54 are constituted by those halves of the tracks 31 facing outwards from the annular chamber 42. The surfaces 53 are closertogetherthan the surfaces 54, and consequently the constraining reactions which pass by way of the balls 28 through the contact surfaces between these latter and the shaft 4 and ring 27, are inclined by a certain angle to the axis of the shaft 4, and diverge in the direction of this latter. Because of the particular construction of the hemispherical tracks 31 and 32, the assembly formed by said tracks and the balls 28 behaves as ah oblique rolling bearing. This enables the two rows of balls to be disposed very close together without overloading the rolling bodies.

This is because the load which acts on the balls of each row is not determined by the distance between their geometrical centres, but by the length of an imaginary segment intersected along the axis of the shaft 4 by the straight lines along which the constraining reactions act when said shaft 4 is stressed.

If the balls 28 roll in tracks which are not offset, the geometrical distance between them and the length of said segment are equal. However, when the tracks 31 and 32 are offset as heretofore described, the length of said segment is greaterthan the geometri cal distance between the two rows of balls, and this means that the load acting on the balls 28 is equal to that which would act on them if they were located at a distance apart which was greater than the geometrical distance, namely a distance equal to the length of said imaginary segment. Thus, by arranging for the constraining reactions to be inclined, the two rows of balls can be brought close together, so considerably reducing the overall axial dimension without increasing the stresses thereon.

In Figure 4, the integral unit 1 of Figure 1 is mounted on the pump casing 50, to form a centrifugal pump 55. The pump casing 50 comprises a suction port 56, a chamber 57 for housing the impeller and communicating with the outside by way of a circular compartment 59, and a delivery port 58. The element 7 seals the casing 50, with which it engages by way of the annular surface 48 which cooperates with the circular compartment 59 provided in said pump casing 50, and is fixed to it by screws 60 housed in the bores 47 and screwed into threaded bores 61.

When in operation, the pulley 3 is rotated to rotate the shaft 4 on the rolling bodies 28 and thus rotate the impeller 2, which draws water in through the port 56 and expels it through the port 58. Any water which infiltrates through the seal assembly 8 from the chamber 57, and thus into the compartment 16, is centrifuged by the ring 44 rigid with the impeller 2, and is expelled from the compartment 16 through the discharge duct 43.

Figure 5 shows a different embodiment of the pumping unit according to the invention. The unit of Figure 5, indicated overall by 62, is similar to the unit 1 of Figure 2, from which it differs only in the type of rolling bodies used. Those details similar or equal to those already described are indicated by the same reference numerals.

The support element 7 comprises a flange portion 11 and a ring portion 27, between which the shaft 4 rotates supported by suitably spaced-apart rolling bodies 63. The rolling bodies 63 comprise a row of balls 64 which roll between a pairoffacing hemispherical tracks 65 provided in an inner surface 33 of the ring portion 27 and in an outer surface 41 of the shaft 4 respectively, and a row of rollers 66 which are positioned by a spacing cage 67 and roll directly on the surfaces 33 and 41. The ring portion 27 is of elongated cylindrical shape to allow the two rows of rolling bodies 63 to be suitably spaced apart. The seal at the end comprising the impeller 2, which is fixed on to one end of the shaft 4, which at its other end carries a toothed pulley 3, is provided by a seal assembly 8 completely similarto that already described, and by a double lip gasket 68.

The unit 62 has a greater overall axial length than the unit 1, but is of more simple construction. However, it is of shorter length than conventional designs both because of the elimination of the outer race of the bearing, which is replaced by the ring portion 27 of the element 7, and because of the arrangement of the seal assembly 8, which does not require locking devices in that it is fixed by said impeller 2, and which exerts a seal directly against a rear surface 19 of the impeller 2 instead of against the front surface of the hub 20 thereof.

The advantages of the present invention are apparent from the foregoing description. In particular, the overall axial length of the integral pumping unit and thus of the entire centrifugal pump is greatly reduced. The construction of an integral unit comprising all the pump elements with the exception of its casing also leads to economy and a greater machining accuracy, and allows rapid and easy maintenance.

From the aforegoing description, it is apparent that modifications can be made to the embodiments of the present invention without leaving the scope of the inventive idea.

In particular, different numbers and types of seal assembly can be used in different positions; the impeller and pulley can be fixed on to the shaft differently; finally the toothed pulley can be replaced by any other motion transmission member.

Claims (12)

1. An integral pumping unit (1, 62) for centrifugal pumps (55), particularly for motor vehicle water pumps, arranged for mounting on a pump casing (50) of said centrifugal pumps (55), characterised by comprising a transmission shaft (4) rotating about its axis and provided at its two ends (5, 6) with a centrifugal impeller (2) and a member (3) for transmitting rotary motion to said shaft (4) respectively, a support element (7) for said shaft (4) provided at one end with a flange portion (11) arranged to seal said pump casing (50) in a fluid-tight manner and facing said impeller (2), two rows of rolling bodies (28,63) disposed between said shaft (4) and said support element (7) to make the former rotatable relative to the latter with low friction, and a plurality of seal assemblies (8, 38, 68) arranged to provide a watertight seal between said shaft (4) and said support element (7), said transmission shaft (4) comprising an outer surface (41) on which said rolling bodies (28, 63) directly roll, and said seal assemblies (8,38, 68) comprising at least one gasket (25) disposed between said impeller (2) and said rolling bodies (28, 63) and urged by resilient means against a rear surface (19) of said impeller (2) in orderto provide a seal between this latter and a socket (22) housed in said support element (7), and in which said gasket (25) is contained.

2. An integral pumping unit (1) as claimed in claim 1, characterised in that said support element (7) and said transmission shaft (4) comprise two pairs of facing tracks (31, 32) between which said rolling bodies (28) roll, each track of each pair of tracks (31, 32) being-axially offset from the track which it faces, in such a manner that the bending stresses on said shaft (4) produce constraining reactions on said rolling bodies (28) directed along oblique straight lines which diverge in the direction of the axis of said shaft.

3. An integral pumping unit (1,62) as claimed in claims 1 or 2, characterised in that said rolling bodies (28,63) roll directly on an inner surface (33) of a ring portion (27) of said support element (7) which is rigid with said flange portion (11), said inner surface (33) facing and being concentric with said outer surface (41) of said shaft.

4. An integral pumping unit (1) as claimed in claim 1 or 2, characterised in that said rolling bodies (28) roll on an inner surface of an outer cylindrical ring (27) which is concentric with said shaft (4) and is fixed into a seat (12) in said support element (7)

5. An integral pumping unit (1) as claimed in claim 2, characterised in that said rolling bodies are balls (28) and are slidable in hemispherical tracks (31,32), of which a first pair (31) is carried bysaid shaft (4) and a second pair (32) is carried by said support element (7), said tracks of said first pair (31) having profiles with axes of symmetry (51) which are spaced apart by a distance (A) which is smaller than the distance (B) between the axes of symmetry (52) of the profiles of said tracks of said second pair (32).

6. An integral pumping unit (1) as claimed in claim 2 or 5, characterised in that said balls (28), which are slidable between said first pair of hemispherical tracks (31) and said second pair of hemispherical tracks (32), have their axes of symmetry (49) perpendicular to said shaft (4) and lying between said axis of symmetry (51) of each of said tracks (31) of said first pair and said axis of symmetry (52) of each of said tracks (32) of said second pair.

7. An integral pumping unit (1) as claimed in one of claims 5 or 6, characterised in that said balls (28) roll on adjacent surfaces (53) pertaining to said second pair of tracks (32), and on surfaces (54) which face outwards from a chamber (42) lying between said shaft (4) and said support element (7) and which pertain to said first pair of tracks (31), said surfaces (53) pertaining to said second pair oftracks (32) being axially closer together than said surfaces (54) pertaining to said first pair of tracks (31).

8. An integral pumping unit (1) as claimed in one of the preceding claims, characterised in that said first pair of tracks (31) is axially offset from said second pairoftracks (32).

9. An integral pumping unit (1,62) as claimed in claim 1, characterised in that said seal assemblies comprise water-tight shields (38) and an assembly (8) comprising a socket (22) of a suitable metal fixed into a seat (21) in said support element (7), a spiral spring housed in said socket (22) and resting against a thrust ring disposed between the spiral spring and a gasket (25) housed in said socket (22) and slidable therein, said gasket (25) being retained in said socket (22) by an annular stop (26) provided thereon, ahd being pressed with a predetermined pressure against said surface of said impeller (2).

10. A pumping unit (1) as claimed in claim 5, characterised in that said outer ring (27) is lightly forced into a cylindrical seat (17) provided in a sleeve portion (12) pertaining to said support element (7), and is locked axially in said seat (12) by a shoulder projection (18) and a setscrew (34).

11. An integral pumping unit (1,62) as claimed in one of the preceding claims, characterised in that an oblique bore (43) is provided in said support element (7) to connect to atmosphere a compartment (16) provided inside said support element (7), said impel ler (2) having fixed thereon a slinger ring (44) for the purpose of evacuating through said bore (43) by centrifugal force any traces of moisture contained in said compartment (16).

12. An integral pumping unit (1) as heretofore described and illustrated on the accompanying drawings.