EP0478514A1

EP0478514A1 - Variable delivery gear pump

Info

Publication number: EP0478514A1
Application number: EP91830381A
Authority: EP
Inventors: Elio Bussi
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-09-26
Filing date: 1991-09-18
Publication date: 1992-04-01
Also published as: IT1241688B; IT9067722A0; IT9067722A1

Abstract

A geared pump (10) with a variable flow rate, in which the gears (14, 16) can slide axially relative to each other, has a pair of cup-shaped sealing elements (36, 40) adapted substantially to fill the spaces between adjacent teeth and having slots (37) in which the tips of the teeth of the gears are disposed.

Description

The present invention relates to a geared pump with a variable flow rate, of the type including a pair of meshed gears which are slidable axially relative to each other and sealing elements, mounted on each gear so as substantially to fill the spaces between adjacent teeth and slidable axially relative to the gears.
A pump of this type is described and illustrated in British patent 1,539,515 to which reference is made herein.
In this known solution, the sealing elements are constituted by discs which have outside diameters larger than the addendum diameters of the gears and are housed in suitable seats in the housing or in end blocks for supporting the gears. As well as being quite complex structurally, this solution requires the use of auxiliary sealing members for preventing the escape of excess liquid from the high-pressure side of the pump to the low-pressure side.
Moreover, in the solution described in the British patent mentioned above, the housing of the pump has to be formed by two shells which are then fitted together, creating possible escape routes for the pumped fluid and increasing the final cost of the product.
The object of the present invention is to provide a pump of the type specified at the beginning of the description which does not have the aforementioned disadvantages and which is simple and cheap to produce.
According to the invention, this object is achieved by virtue of the fact that each sealing element of the pump is substantially cup-shaped with an outside diameter substantially equal to the addendum diameter of the corresponding gear, the side wall of each sealing element having a plurality of axial slots in which the tips of the teeth of the respective gear are disposed.
By virtue of these characteristics, the housing of the pump, which is substantially identical to that used for constant-flow geared pumps, is considerably simpler to produce and, moreover, the use of an auxiliary sealing member is not necessary and the product is therefore more reliable and cheaper.
The end faces of each gear are sealed against an end support block and an end face of the cup-shaped sealing element.
Further advantages and characteristics of the pump according to the invention will become clear from the detailed description which follows purely by way of non-limiting example, with reference to the appended drawings, in which:

Figure 1 is a transparent, perspective view of a pump according to the invention showing its internal members,
Figure 2 is an exploded perspective view of the pump of Figure 1,
Figure 3 is a schematic cross-section of the pump in a minimum flow configuration, and
Figure 4 is a view similar to Figure 3, showing the pump in its maximum flow configuration.

With reference to the drawings, a geared pump with a variable flow rate, generally indicated 10, includes a housing 12 in which a drive gear 14 and a driven gear 16 are rotatable.
The housing 12 has a central element 12a with an inlet aperture 18 and an outlet aperture 20. The central element 12a is closed at its ends by a first plate 12b and a second plate 12c which are clamped to the central portion 12a by tie bolts 22.
A first support block 24 fixed to the first plate 12b, has a figure-eight-shaped cross-section corresponding to the shape of the cavity in the housing and including a first tubular portion 24a with an arcuate notch 25 and a second tubular portion 24b which is shorter than the first and partially fits in the arcuate notch 25. A second support block 26 including a first tubular portion 26a which also has an arcuate notch 27, and a second tubular portion 26b shorter than the first, is similarly slidable in the central portion 12a of the housing 12.
A shaft 28 for driving the drive gear 14 and an idle shaft 30 for the driven shaft 16 are rotatable in the support blocks 24 and 26, respectively. The shaft 28 has an end 28a which is outside the first plate 12b of the housing 12, and to which a gear 32 for driving the pump is keyed. The shaft 28 also has a portion 28b which is rotatable in the first tubular portion 24a of the support block 24 and a further portion 28c which is rotatable in the second tubular portion 26b of the support block 26. A first cup-shaped sealing element 36, interposed between the drive gear 14 and the second support block 26, has a cavity the shape of which corresponds substantially to that of the gear 14, and has a hole 36a the diameter of which corresponds to that of the portion 28c of the shaft 28. The cavity complementary to the shape of the gear 14 is produced in the first sealing element 36, for example, by electroerosion, and communicates with the side face of the element, indicated 36b in the drawings, through a plurality of axial slots 37 in which the tips 14a of the teeth of the gear 14 are disposed. In other words, the outside diameter of the first sealing element 36 is identical to the addendum diameter of the gear 14. A helical spring 38, whose function will become clear from the following description, is also interposed between the gear 14 and the first sealing element 36.
The difference between the lengths of the tubular elements 24a and 24b of the first support block 24 corresponds to the length of the first sealing element 36.
A second sealing element 40, identical in shape to the first sealing element, is interposed in a manner similar to that described above between the second tubular portion 24b of the first support block 24 and the driven gear 16 and also has a central hole 40a, for sliding on a portion 30a of the shaft 30, and a lateral surface 40b with a plurality of axial slots 37 in which the tips of the teeth of the driven gear 16 are disposed. A second portion 30b of the shaft 30 of the driven gear 16 is rotatable and slidable in the first tubular portion 26a of the second support block 26. A helical spring 42, whose function will become clear from the following description, is also interposed between the second sealing element 40 and the driven gear 16.
The difference between the lengths of the tubular elements 26 and 26b of the second support block 26 corresponds to the length of the second sealing element 40, which is the same as the length of the first sealing element 36.
Two springs 46 are interposed between the second support block 26 and the second closure plate 12c of the housing 12 for urging the second support block 26 towards the first closure plate 12b. A screw element 48 is inserted through a central hole 50 in the second closure plate 12c and cooperates with a threaded seat 48a in the support block 26 to adjust the axial position of the second block 26 within the housing 12.
The operation of the pump 10 is illustrated clearly in Figure 1 and in Figures 3 and 4. Figure 3 shows a configuration of minimum meshing between the gears 14 and 16 and hence of minimum flow rate of the pump. In this configuration, as in the intermediate and maximum flow-rate configurations, the end surface of the first sealing element 36 opposite the hole 36a is in contact with the sides of the teeth of the driven gear 16. Similarly, the end portion of the second sealing element 40 opposite the hole 40a and indicated A in the drawings, is in contact with the sides of the teeth of the drive gear 14. In the minimum flow-rate configuration of Figure 3, the second support block 26 is in the position in which it is inserted furthest into the housing 12 and the first and second sealing elements 36 and 40 are in the configuration of maximum "coverage" of the respective gears 14 and 16. In this configuration, by virtue of the action of the spring 42, the shaft 30 of the driven gear 16 is in its axial position nearest the closure plate 12b (the furthest towards the left with reference to Figure 3). Clearly, in this configuration, the seal between the high- and low-pressure regions of the pump is achieved directly against the internal surface of the housing 12, against the end surfaces of the portions 24a and 26a of the support blocks 24 and 26, and in correspondence with the end surfaces of the sealing elements 36 and 40.
The operation of the screw element 48 slides the second support block 26 towards the closure plate 12c against the action of the springs 46. An intermediate flow-rate configuration is shown, for example, in Figure 1.
Figure 4 shows the configuration of maximum meshing and hence of maximum flow-rate. In this configuration, the second support block 26 is substantially adjacent the second closure plate 12c and the sealing elements 36 and 40 are in the position of minimum coverage of the gears 14 and 16. The helical spring 38 keeps the first sealing element 36 substantially in contact with the end surface of the tubular portion 26b of the second support block 26 whilst the helical spring 42 keeps the shaft 30 of the driven gear 16 in the axial position furthest from the first closure plate 12b of the housing 12.
Naturally, the sliding of the second support block 26 and of the shaft 30 associated therewith, which varies the flow rate, may be achieved in a manner other than that described above.
Clearly, for the pump to operate well, it must have ducts for the lubrication of the friction surfaces and for the taking-up of any play; for simplicity, the ducts, the use and location of which are within the general knowledge of an average expert in the art, have not been shown in the drawings.
Moreover it is intended that, the principle of the invention remaining the same, the details of construction and forms of embodiment may be varied widely with respect to those described and illustrated in the drawings, without thereby departing from the scope of the present invention.
For example, instead of being formed by a single body, each sealing element may include a plurality of shaped bars (as many as the teeth of the respective gear) which, with the tips of the teeth of each gear, can define a continuous cylindrical surface with a diameter equal to the addendum diameter of the gear.

Claims

A geared pump with a variable flow rate, of the type including a pair of meshed gears slidable axially relative to each other and sealing elements, mounted on each gear so as substantially to fill the spaces between adjacent gears, and slidable axially relative to the gears, characterised in that each sealing element (36, 40) is substantially cup-shaped with an outside diameter substantially equal to the addendum diameter of the corresponding gear (14, 16) the side wall (36b, 40b) of each sealing element (36, 40) having a plurality of axial slots (37) in which the tips (14a, 16a) of the teeth of the respective gears (14, 16) are disposed.
A geared pump according to Claim 1, characterised in that it includes a pair of blocks (24, 26) for supporting the shafts (28, 30) of the gears (14, 16), the blocks being disposed within the housing (12) of the pump and at least one block (26) being movable axially relative to the housing (12a) so as to slide the gears (14, 16) axially relative to each other.
A geared pump with a variable flow-rate of the type including a pair of meshed gears slidable axially relative to each other and sealing elements, mounted on each gear so as substantially to fill the spaces between adjacent teeth, and slidable axially relative to the gears, characterised in that each sealing element includes a plurality of shaped bars defining, with the tips of the teeth of each gear (14, 16) a substantially continuous cylindrical surface.